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 $249.76   10.549%   $276.1072   $276.11   $276.10   $276.10  
  Purchase #2 $206.66   6.393%   $219.8718   $219.87   $219.85   $219.90  
  Purchase #3 $159.29   11.829%   $178.1324   $178.13   $178.15   $178.10  
  Purchase #4 $58.73   3.120%   $60.5624   $60.56   $60.55   $60.60  
  Purchase #5 $88.34   7.607%   $95.06   $95.06   $95.05   $95.10  
  Purchase #6 $239.89   11.785%   $268.161   $268.16   $268.15   $268.20  
  Purchase #7 $164.37   6.226%   $174.6037   $174.60   $174.60   $174.60  
  7 purchase totals = $1,167.04       $1,272.4985   $1,272.49   $1,272.45   $1,272.60