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 $70.53   7.713%   $75.97   $75.97   $75.95   $76.00  
  Purchase #2 $236.74   11.674%   $264.377   $264.38   $264.40   $264.40  
  Purchase #3 $245.54   4.659%   $256.9797   $256.98   $257.00   $257.00  
  Purchase #4 $234.57   6.474%   $249.7561   $249.76   $249.75   $249.80  
  Purchase #5 $46.94   13.188%   $53.1304   $53.13   $53.15   $53.10  
  Purchase #6 $73.86   11.683%   $82.4891   $82.49   $82.50   $82.50  
  Purchase #7 $193.99   4.491%   $202.7021   $202.70   $202.70   $202.70  
  7 purchase totals = $1,102.17       $1,185.4044   $1,185.41   $1,185.45   $1,185.50