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 $245.97   12.573%   $276.8958   $276.90   $276.90   $276.90  
  Purchase #2 $203.84   9.581%   $223.3699   $223.37   $223.35   $223.40  
  Purchase #3 $159.50   9.504%   $174.6589   $174.66   $174.65   $174.70  
  Purchase #4 $126.54   5.733%   $133.7945   $133.79   $133.80   $133.80  
  Purchase #5 $210.95   3.192%   $217.6835   $217.68   $217.70   $217.70  
  Purchase #6 $85.83   5.689%   $90.7129   $90.71   $90.70   $90.70  
  Purchase #7 $130.97   10.241%   $144.3826   $144.38   $144.40   $144.40  
  7 purchase totals = $1,163.60       $1,261.4981   $1,261.49   $1,261.50   $1,261.60