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 $109.92   8.468%   $119.228   $119.23   $119.25   $119.20  
  Purchase #2 $58.33   10.306%   $64.3415   $64.34   $64.35   $64.30  
  Purchase #3 $121.94   6.545%   $129.921   $129.92   $129.90   $129.90  
  Purchase #4 $97.54   9.198%   $106.5117   $106.51   $106.50   $106.50  
  Purchase #5 $146.92   10.570%   $162.4494   $162.45   $162.45   $162.40  
  Purchase #6 $169.32   11.691%   $189.1152   $189.12   $189.10   $189.10  
  Purchase #7 $162.41   9.621%   $178.0355   $178.04   $178.05   $178.00  
  7 purchase totals = $866.38       $949.6023   $949.61   $949.60   $949.40