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 $208.36   11.767%   $232.8777   $232.88   $232.90   $232.90  
  Purchase #2 $166.73   9.269%   $182.1842   $182.18   $182.20   $182.20  
  Purchase #3 $54.80   7.541%   $58.9325   $58.93   $58.95   $58.90  
  Purchase #4 $100.72   6.572%   $107.3393   $107.34   $107.35   $107.30  
  Purchase #5 $139.74   6.534%   $148.8706   $148.87   $148.85   $148.90  
  Purchase #6 $58.88   6.770%   $62.8662   $62.87   $62.85   $62.90  
  Purchase #7 $126.91   10.671%   $140.4526   $140.45   $140.45   $140.50  
  7 purchase totals = $856.14       $933.5231   $933.52   $933.55   $933.60