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 $83.89   11.199%   $93.2848   $93.28   $93.30   $93.30  
  Purchase #2 $157.98   9.488%   $172.9691   $172.97   $172.95   $173.00  
  Purchase #3 $213.53   5.307%   $224.862   $224.86   $224.85   $224.90  
  Purchase #4 $44.49   13.395%   $50.4494   $50.45   $50.45   $50.40  
  Purchase #5 $84.40   8.709%   $91.7504   $91.75   $91.75   $91.80  
  Purchase #6 $185.33   13.868%   $211.0316   $211.03   $211.05   $211.00  
  Purchase #7 $67.63   7.537%   $72.7273   $72.73   $72.75   $72.70  
  7 purchase totals = $837.25       $917.0746   $917.07   $917.10   $917.10