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 $118.29   6.243%   $125.6748   $125.67   $125.65   $125.70  
  Purchase #2 $162.84   10.836%   $180.4853   $180.49   $180.50   $180.50  
  Purchase #3 $134.97   8.326%   $146.2076   $146.21   $146.20   $146.20  
  Purchase #4 $234.38   5.667%   $247.6623   $247.66   $247.65   $247.70  
  Purchase #5 $199.30   5.638%   $210.5365   $210.54   $210.55   $210.50  
  Purchase #6 $195.28   8.205%   $211.3027   $211.30   $211.30   $211.30  
  Purchase #7 $214.27   11.622%   $239.1725   $239.17   $239.15   $239.20  
  7 purchase totals = $1,259.33       $1,361.0417   $1,361.04   $1,361.00   $1,361.10