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 $54.92   11.707%   $61.3495   $61.35   $61.35   $61.30  
  Purchase #2 $59.58   6.337%   $63.3556   $63.36   $63.35   $63.40  
  Purchase #3 $215.96   7.374%   $231.8849   $231.88   $231.90   $231.90  
  Purchase #4 $98.61   7.629%   $106.133   $106.13   $106.15   $106.10  
  Purchase #5 $146.89   7.796%   $158.3415   $158.34   $158.35   $158.30  
  Purchase #6 $154.67   4.507%   $161.641   $161.64   $161.65   $161.60  
  Purchase #7 $65.28   11.152%   $72.56   $72.56   $72.55   $72.60  
  7 purchase totals = $795.91       $855.2655   $855.26   $855.30   $855.20