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 $54.94   3.675%   $56.959   $56.96   $56.95   $57.00  
  Purchase #2 $96.28   6.308%   $102.3533   $102.35   $102.35   $102.40  
  Purchase #3 $15.38   11.303%   $17.1184   $17.12   $17.10   $17.10  
  Purchase #4 $190.36   8.463%   $206.4702   $206.47   $206.45   $206.50  
  Purchase #5 $153.45   10.618%   $169.7433   $169.74   $169.75   $169.70  
  Purchase #6 $185.79   10.407%   $205.1252   $205.13   $205.15   $205.10  
  Purchase #7 $5.69   6.726%   $6.0727   $6.07   $6.05   $6.10  
  7 purchase totals = $701.89       $763.8421   $763.84   $763.80   $763.90