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 $245.50   12.323%   $275.753   $275.75   $275.75   $275.80  
  Purchase #2 $96.63   12.490%   $108.6991   $108.70   $108.70   $108.70  
  Purchase #3 $100.45   6.776%   $107.2565   $107.26   $107.25   $107.30  
  Purchase #4 $74.40   4.216%   $77.5367   $77.54   $77.55   $77.50  
  Purchase #5 $129.51   5.308%   $136.3844   $136.38   $136.40   $136.40  
  Purchase #6 $25.79   5.706%   $27.2616   $27.26   $27.25   $27.30  
  Purchase #7 $162.72   4.218%   $169.5835   $169.58   $169.60   $169.60  
  7 purchase totals = $835.00       $902.4748   $902.47   $902.50   $902.60