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 $53.95   11.202%   $59.9935   $59.99   $60.00   $60.00  
  Purchase #2 $74.50   13.226%   $84.3534   $84.35   $84.35   $84.40  
  Purchase #3 $79.33   7.135%   $84.9902   $84.99   $85.00   $85.00  
  Purchase #4 $81.54   8.690%   $88.6258   $88.63   $88.65   $88.60  
  Purchase #5 $176.54   11.492%   $196.828   $196.83   $196.85   $196.80  
  Purchase #6 $169.53   6.234%   $180.0985   $180.10   $180.10   $180.10  
  Purchase #7 $81.84   12.437%   $92.0184   $92.02   $92.00   $92.00  
  7 purchase totals = $717.23       $786.9078   $786.91   $786.95   $786.90