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 $10.93   4.764%   $11.4507   $11.45   $11.45   $11.50  
  Purchase #2 $221.53   3.449%   $229.1706   $229.17   $229.15   $229.20  
  Purchase #3 $169.62   5.607%   $179.1306   $179.13   $179.15   $179.10  
  Purchase #4 $239.39   8.728%   $260.284   $260.28   $260.30   $260.30  
  Purchase #5 $150.41   6.719%   $160.516   $160.52   $160.50   $160.50  
  Purchase #6 $216.97   9.293%   $237.133   $237.13   $237.15   $237.10  
  Purchase #7 $69.97   10.215%   $77.1174   $77.12   $77.10   $77.10  
  7 purchase totals = $1,078.82       $1,154.8023   $1,154.80   $1,154.80   $1,154.80