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 $86.66   9.788%   $95.1423   $95.14   $95.15   $95.10  
  Purchase #2 $143.48   13.430%   $162.7494   $162.75   $162.75   $162.70  
  Purchase #3 $129.75   6.503%   $138.1876   $138.19   $138.20   $138.20  
  Purchase #4 $121.35   3.858%   $126.0317   $126.03   $126.05   $126.00  
  Purchase #5 $14.65   11.614%   $16.3515   $16.35   $16.35   $16.40  
  Purchase #6 $215.45   5.118%   $226.4767   $226.48   $226.50   $226.50  
  Purchase #7 $209.43   7.418%   $224.9655   $224.97   $224.95   $225.00  
  7 purchase totals = $920.77       $989.9047   $989.91   $989.95   $989.90