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 $39.32   12.843%   $44.3699   $44.37   $44.35   $44.40  
  Purchase #2 $115.68   13.457%   $131.2471   $131.25   $131.25   $131.20  
  Purchase #3 $121.72   12.169%   $136.5321   $136.53   $136.55   $136.50  
  Purchase #4 $237.29   10.198%   $261.4888   $261.49   $261.50   $261.50  
  Purchase #5 $97.59   9.665%   $107.0221   $107.02   $107.00   $107.00  
  Purchase #6 $191.82   8.376%   $207.8868   $207.89   $207.90   $207.90  
  Purchase #7 $23.27   9.300%   $25.4341   $25.43   $25.45   $25.40  
  7 purchase totals = $826.69       $913.9809   $913.98   $914.00   $913.90