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 $118.54   12.531%   $133.3942   $133.39   $133.40   $133.40  
  Purchase #2 $182.80   8.251%   $197.8828   $197.88   $197.90   $197.90  
  Purchase #3 $160.88   6.758%   $171.7523   $171.75   $171.75   $171.80  
  Purchase #4 $20.56   11.279%   $22.879   $22.88   $22.90   $22.90  
  Purchase #5 $199.72   6.724%   $213.1492   $213.15   $213.15   $213.10  
  Purchase #6 $71.95   6.177%   $76.3944   $76.39   $76.40   $76.40  
  Purchase #7 $194.55   7.525%   $209.1899   $209.19   $209.20   $209.20  
  7 purchase totals = $949.00       $1,024.6418   $1,024.63   $1,024.70   $1,024.70