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 $126.38   11.252%   $140.6003   $140.60   $140.60   $140.60  
  Purchase #2 $172.86   13.289%   $195.8314   $195.83   $195.85   $195.80  
  Purchase #3 $18.88   8.798%   $20.5411   $20.54   $20.55   $20.50  
  Purchase #4 $161.45   13.231%   $182.8114   $182.81   $182.80   $182.80  
  Purchase #5 $22.44   4.284%   $23.4013   $23.40   $23.40   $23.40  
  Purchase #6 $85.93   6.707%   $91.6933   $91.69   $91.70   $91.70  
  Purchase #7 $223.49   7.131%   $239.4271   $239.43   $239.45   $239.40  
  7 purchase totals = $811.43       $894.3059   $894.30   $894.35   $894.20