Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $97.99   13.206%   $110.9306   $110.93   $110.95   $110.90  
  Purchase #2 $183.35   10.375%   $202.3726   $202.37   $202.35   $202.40  
  Purchase #3 $158.96   13.162%   $179.8823   $179.88   $179.90   $179.90  
  Purchase #4 $91.89   11.411%   $102.3756   $102.38   $102.40   $102.40  
  Purchase #5 $237.65   8.506%   $257.8645   $257.86   $257.85   $257.90  
  Purchase #6 $150.97   3.398%   $156.1   $156.10   $156.10   $156.10  
  Purchase #7 $31.67   7.360%   $34.0009   $34.00   $34.00   $34.00  
  7 purchase totals = $952.48       $1,043.5265   $1,043.52   $1,043.55   $1,043.60