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 $61.46   11.305%   $68.4081   $68.41   $68.40   $68.40  
  Purchase #2 $174.51   13.650%   $198.3306   $198.33   $198.35   $198.30  
  Purchase #3 $173.42   12.207%   $194.5894   $194.59   $194.60   $194.60  
  Purchase #4 $118.30   6.561%   $126.0617   $126.06   $126.05   $126.10  
  Purchase #5 $100.94   9.653%   $110.6837   $110.68   $110.70   $110.70  
  Purchase #6 $119.62   13.733%   $136.0474   $136.05   $136.05   $136.00  
  Purchase #7 $164.71   10.583%   $182.1413   $182.14   $182.15   $182.10  
  7 purchase totals = $912.96       $1,016.2622   $1,016.26   $1,016.30   $1,016.20