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 $48.76   9.158%   $53.2254   $53.23   $53.25   $53.20  
  Purchase #2 $61.52   8.758%   $66.9079   $66.91   $66.90   $66.90  
  Purchase #3 $106.36   9.840%   $116.8258   $116.83   $116.85   $116.80  
  Purchase #4 $6.87   5.712%   $7.2624   $7.26   $7.25   $7.30  
  Purchase #5 $184.78   4.785%   $193.6217   $193.62   $193.60   $193.60  
  Purchase #6 $244.37   8.139%   $264.2593   $264.26   $264.25   $264.30  
  Purchase #7 $114.87   4.232%   $119.7313   $119.73   $119.75   $119.70  
  7 purchase totals = $767.53       $821.8338   $821.84   $821.85   $821.80