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 $44.89   13.427%   $50.9174   $50.92   $50.90   $50.90  
  Purchase #2 $195.88   13.484%   $222.2925   $222.29   $222.30   $222.30  
  Purchase #3 $73.28   8.866%   $79.777   $79.78   $79.80   $79.80  
  Purchase #4 $231.97   12.681%   $261.3861   $261.39   $261.40   $261.40  
  Purchase #5 $110.39   7.607%   $118.7874   $118.79   $118.80   $118.80  
  Purchase #6 $53.77   12.148%   $60.302   $60.30   $60.30   $60.30  
  Purchase #7 $45.25   9.695%   $49.637   $49.64   $49.65   $49.60  
  7 purchase totals = $755.43       $843.0994   $843.11   $843.15   $843.10