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 $62.65   8.540%   $68.0003   $68.00   $68.00   $68.00  
  Purchase #2 $48.40   9.467%   $52.982   $52.98   $53.00   $53.00  
  Purchase #3 $198.28   12.429%   $222.9242   $222.92   $222.90   $222.90  
  Purchase #4 $33.76   6.625%   $35.9966   $36.00   $36.00   $36.00  
  Purchase #5 $65.70   12.449%   $73.879   $73.88   $73.90   $73.90  
  Purchase #6 $71.99   11.297%   $80.1227   $80.12   $80.10   $80.10  
  Purchase #7 $72.26   13.655%   $82.1271   $82.13   $82.15   $82.10  
  7 purchase totals = $553.04       $616.0319   $616.03   $616.05   $616.00