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 $153.81   8.797%   $167.3407   $167.34   $167.35   $167.30  
  Purchase #2 $53.42   11.751%   $59.6974   $59.70   $59.70   $59.70  
  Purchase #3 $88.44   8.773%   $96.1988   $96.20   $96.20   $96.20  
  Purchase #4 $106.63   5.298%   $112.2793   $112.28   $112.30   $112.30  
  Purchase #5 $177.80   9.597%   $194.8635   $194.86   $194.85   $194.90  
  Purchase #6 $188.53   11.246%   $209.7321   $209.73   $209.75   $209.70  
  Purchase #7 $114.61   13.575%   $130.1683   $130.17   $130.15   $130.20  
  7 purchase totals = $883.24       $970.2801   $970.28   $970.30   $970.30