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 $65.86   4.753%   $68.9903   $68.99   $69.00   $69.00  
  Purchase #2 $208.75   5.856%   $220.9744   $220.97   $220.95   $221.00  
  Purchase #3 $75.67   11.687%   $84.5136   $84.51   $84.50   $84.50  
  Purchase #4 $125.41   3.311%   $129.5623   $129.56   $129.55   $129.60  
  Purchase #5 $206.37   7.595%   $222.0438   $222.04   $222.05   $222.00  
  Purchase #6 $62.84   5.647%   $66.3886   $66.39   $66.40   $66.40  
  Purchase #7 $184.86   3.285%   $190.9327   $190.93   $190.95   $190.90  
  7 purchase totals = $929.76       $983.4057   $983.39   $983.40   $983.40