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 $87.41   12.401%   $98.2497   $98.25   $98.25   $98.20  
  Purchase #2 $25.87   12.860%   $29.1969   $29.20   $29.20   $29.20  
  Purchase #3 $69.69   7.389%   $74.8394   $74.84   $74.85   $74.80  
  Purchase #4 $248.88   4.776%   $260.7665   $260.77   $260.75   $260.80  
  Purchase #5 $162.83   7.434%   $174.9348   $174.93   $174.95   $174.90  
  Purchase #6 $46.26   8.226%   $50.0653   $50.07   $50.05   $50.10  
  Purchase #7 $108.40   4.546%   $113.3279   $113.33   $113.35   $113.30  
  7 purchase totals = $749.34       $801.3805   $801.39   $801.40   $801.30