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 $107.98   8.103%   $116.7296   $116.73   $116.75   $116.70  
  Purchase #2 $192.98   11.606%   $215.3773   $215.38   $215.40   $215.40  
  Purchase #3 $103.51   8.243%   $112.0423   $112.04   $112.05   $112.00  
  Purchase #4 $225.52   4.860%   $236.4803   $236.48   $236.50   $236.50  
  Purchase #5 $134.91   11.632%   $150.6027   $150.60   $150.60   $150.60  
  Purchase #6 $161.84   3.107%   $166.8684   $166.87   $166.85   $166.90  
  Purchase #7 $247.53   5.739%   $261.7357   $261.74   $261.75   $261.70  
  7 purchase totals = $1,174.27       $1,259.8363   $1,259.84   $1,259.90   $1,259.80