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 $130.86   12.142%   $146.749   $146.75   $146.75   $146.70  
  Purchase #2 $239.54   4.756%   $250.9325   $250.93   $250.95   $250.90  
  Purchase #3 $160.70   4.222%   $167.4848   $167.48   $167.50   $167.50  
  Purchase #4 $215.55   13.839%   $245.38   $245.38   $245.40   $245.40  
  Purchase #5 $174.64   3.554%   $180.8467   $180.85   $180.85   $180.80  
  Purchase #6 $64.99   13.725%   $73.9099   $73.91   $73.90   $73.90  
  Purchase #7 $187.72   9.833%   $206.1785   $206.18   $206.20   $206.20  
  7 purchase totals = $1,174.00       $1,271.4814   $1,271.48   $1,271.55   $1,271.40