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 $55.85   13.699%   $63.5009   $63.50   $63.50   $63.50  
  Purchase #2 $84.37   13.305%   $95.5954   $95.60   $95.60   $95.60  
  Purchase #3 $107.73   11.614%   $120.2418   $120.24   $120.25   $120.20  
  Purchase #4 $116.46   8.310%   $126.1378   $126.14   $126.15   $126.10  
  Purchase #5 $173.94   12.216%   $195.1885   $195.19   $195.20   $195.20  
  Purchase #6 $205.75   9.686%   $225.6789   $225.68   $225.70   $225.70  
  Purchase #7 $70.31   8.368%   $76.1935   $76.19   $76.20   $76.20  
  7 purchase totals = $814.41       $902.5368   $902.54   $902.60   $902.50