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 $103.76   12.137%   $116.3534   $116.35   $116.35   $116.40  
  Purchase #2 $62.53   9.803%   $68.6598   $68.66   $68.65   $68.70  
  Purchase #3 $199.96   7.658%   $215.2729   $215.27   $215.25   $215.30  
  Purchase #4 $53.89   3.692%   $55.8796   $55.88   $55.90   $55.90  
  Purchase #5 $80.74   8.429%   $87.5456   $87.55   $87.55   $87.50  
  Purchase #6 $99.90   3.138%   $103.0349   $103.03   $103.05   $103.00  
  Purchase #7 $207.47   10.801%   $229.8788   $229.88   $229.90   $229.90  
  7 purchase totals = $808.25       $876.6250   $876.62   $876.65   $876.70