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 $59.43   11.278%   $66.1325   $66.13   $66.15   $66.10  
  Purchase #2 $159.87   10.330%   $176.3846   $176.38   $176.40   $176.40  
  Purchase #3 $195.29   10.696%   $216.1782   $216.18   $216.20   $216.20  
  Purchase #4 $209.31   13.472%   $237.5082   $237.51   $237.50   $237.50  
  Purchase #5 $22.93   10.519%   $25.342   $25.34   $25.35   $25.30  
  Purchase #6 $9.40   9.844%   $10.3253   $10.33   $10.35   $10.30  
  Purchase #7 $163.41   9.141%   $178.3473   $178.35   $178.35   $178.30  
  7 purchase totals = $819.64       $910.2181   $910.22   $910.30   $910.10