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 $92.41   9.497%   $101.1862   $101.19   $101.20   $101.20  
  Purchase #2 $68.63   13.713%   $78.0412   $78.04   $78.05   $78.00  
  Purchase #3 $181.90   13.626%   $206.6857   $206.69   $206.70   $206.70  
  Purchase #4 $76.68   7.265%   $82.2508   $82.25   $82.25   $82.30  
  Purchase #5 $245.45   8.761%   $266.9539   $266.95   $266.95   $267.00  
  Purchase #6 $97.93   3.270%   $101.1323   $101.13   $101.15   $101.10  
  Purchase #7 $169.87   7.755%   $183.0434   $183.04   $183.05   $183.00  
  7 purchase totals = $932.87       $1,019.2935   $1,019.29   $1,019.35   $1,019.30