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 $62.95   6.726%   $67.184   $67.18   $67.20   $67.20  
  Purchase #2 $39.32   13.591%   $44.664   $44.66   $44.65   $44.70  
  Purchase #3 $208.54   8.312%   $225.8738   $225.87   $225.85   $225.90  
  Purchase #4 $171.34   9.425%   $187.4888   $187.49   $187.50   $187.50  
  Purchase #5 $139.85   6.655%   $149.157   $149.16   $149.15   $149.20  
  Purchase #6 $96.42   5.796%   $102.0085   $102.01   $102.00   $102.00  
  Purchase #7 $116.33   6.830%   $124.2753   $124.28   $124.30   $124.30  
  7 purchase totals = $834.75       $900.6514   $900.65   $900.65   $900.80