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 $173.32   11.839%   $193.8394   $193.84   $193.85   $193.80  
  Purchase #2 $206.47   9.302%   $225.6758   $225.68   $225.70   $225.70  
  Purchase #3 $37.34   6.800%   $39.8791   $39.88   $39.90   $39.90  
  Purchase #4 $157.53   8.399%   $170.7609   $170.76   $170.75   $170.80  
  Purchase #5 $65.89   3.260%   $68.038   $68.04   $68.05   $68.00  
  Purchase #6 $94.86   13.613%   $107.7733   $107.77   $107.75   $107.80  
  Purchase #7 $146.65   8.331%   $158.8674   $158.87   $158.85   $158.90  
  7 purchase totals = $882.06       $964.8339   $964.84   $964.85   $964.90