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 $85.29   11.237%   $94.874   $94.87   $94.85   $94.90  
  Purchase #2 $209.64   9.761%   $230.103   $230.10   $230.10   $230.10  
  Purchase #3 $67.56   12.352%   $75.905   $75.91   $75.90   $75.90  
  Purchase #4 $124.86   12.126%   $140.0005   $140.00   $140.00   $140.00  
  Purchase #5 $78.38   6.703%   $83.6338   $83.63   $83.65   $83.60  
  Purchase #6 $135.92   9.667%   $149.0594   $149.06   $149.05   $149.10  
  Purchase #7 $185.27   13.551%   $210.3759   $210.38   $210.40   $210.40  
  7 purchase totals = $886.92       $983.9516   $983.95   $983.95   $984.00