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 $245.87   7.659%   $264.7012   $264.70   $264.70   $264.70  
  Purchase #2 $169.58   8.844%   $184.5777   $184.58   $184.60   $184.60  
  Purchase #3 $94.40   10.410%   $104.227   $104.23   $104.25   $104.20  
  Purchase #4 $241.38   6.261%   $256.4928   $256.49   $256.50   $256.50  
  Purchase #5 $247.97   8.151%   $268.182   $268.18   $268.20   $268.20  
  Purchase #6 $169.36   3.703%   $175.6314   $175.63   $175.65   $175.60  
  Purchase #7 $108.57   3.794%   $112.6891   $112.69   $112.70   $112.70  
  7 purchase totals = $1,277.13       $1,366.5012   $1,366.50   $1,366.60   $1,366.50