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 $195.44   4.287%   $203.8185   $203.82   $203.80   $203.80  
  Purchase #2 $171.75   11.517%   $191.5304   $191.53   $191.55   $191.50  
  Purchase #3 $239.68   7.165%   $256.8531   $256.85   $256.85   $256.90  
  Purchase #4 $76.78   4.690%   $80.381   $80.38   $80.40   $80.40  
  Purchase #5 $159.62   4.541%   $166.8683   $166.87   $166.85   $166.90  
  Purchase #6 $62.75   3.149%   $64.726   $64.73   $64.75   $64.70  
  Purchase #7 $44.40   9.756%   $48.7317   $48.73   $48.75   $48.70  
  7 purchase totals = $950.42       $1,012.9090   $1,012.91   $1,012.95   $1,012.90