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 $225.67   13.569%   $256.2912   $256.29   $256.30   $256.30  
  Purchase #2 $104.82   3.259%   $108.2361   $108.24   $108.25   $108.20  
  Purchase #3 $119.30   7.230%   $127.9254   $127.93   $127.95   $127.90  
  Purchase #4 $193.42   4.699%   $202.5088   $202.51   $202.50   $202.50  
  Purchase #5 $228.88   11.739%   $255.7482   $255.75   $255.75   $255.70  
  Purchase #6 $159.87   6.433%   $170.1544   $170.15   $170.15   $170.20  
  Purchase #7 $42.27   11.174%   $46.9932   $46.99   $47.00   $47.00  
  7 purchase totals = $1,074.23       $1,167.8573   $1,167.86   $1,167.90   $1,167.80