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 $59.51   5.103%   $62.5468   $62.55   $62.55   $62.50  
  Purchase #2 $153.52   4.755%   $160.8199   $160.82   $160.80   $160.80  
  Purchase #3 $185.64   8.484%   $201.3897   $201.39   $201.40   $201.40  
  Purchase #4 $30.63   6.634%   $32.662   $32.66   $32.65   $32.70  
  Purchase #5 $219.67   8.331%   $237.9707   $237.97   $237.95   $238.00  
  Purchase #6 $95.36   7.664%   $102.6684   $102.67   $102.65   $102.70  
  Purchase #7 $87.64   5.537%   $92.4926   $92.49   $92.50   $92.50  
  7 purchase totals = $831.97       $890.5501   $890.55   $890.50   $890.60