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 $195.63   8.284%   $211.836   $211.84   $211.85   $211.80  
  Purchase #2 $62.31   4.279%   $64.9762   $64.98   $65.00   $65.00  
  Purchase #3 $62.54   10.766%   $69.2731   $69.27   $69.25   $69.30  
  Purchase #4 $240.68   7.385%   $258.4542   $258.45   $258.45   $258.50  
  Purchase #5 $47.75   5.341%   $50.3003   $50.30   $50.30   $50.30  
  Purchase #6 $217.78   13.380%   $246.919   $246.92   $246.90   $246.90  
  Purchase #7 $30.48   3.766%   $31.6279   $31.63   $31.65   $31.60  
  7 purchase totals = $857.17       $933.3867   $933.39   $933.40   $933.40