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 $86.34   13.739%   $98.2023   $98.20   $98.20   $98.20  
  Purchase #2 $45.97   7.871%   $49.5883   $49.59   $49.60   $49.60  
  Purchase #3 $237.40   7.616%   $255.4804   $255.48   $255.50   $255.50  
  Purchase #4 $69.83   6.227%   $74.1783   $74.18   $74.20   $74.20  
  Purchase #5 $90.41   9.761%   $99.2349   $99.23   $99.25   $99.20  
  Purchase #6 $13.44   6.816%   $14.3561   $14.36   $14.35   $14.40  
  Purchase #7 $161.75   4.596%   $169.184   $169.18   $169.20   $169.20  
  7 purchase totals = $705.14       $760.2243   $760.22   $760.30   $760.30