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 $231.40   12.874%   $261.1904   $261.19   $261.20   $261.20  
  Purchase #2 $118.87   4.726%   $124.4878   $124.49   $124.50   $124.50  
  Purchase #3 $180.68   9.443%   $197.7416   $197.74   $197.75   $197.70  
  Purchase #4 $190.87   13.817%   $217.2425   $217.24   $217.25   $217.20  
  Purchase #5 $91.70   13.173%   $103.7796   $103.78   $103.80   $103.80  
  Purchase #6 $231.65   8.423%   $251.1619   $251.16   $251.15   $251.20  
  Purchase #7 $109.51   8.632%   $118.9629   $118.96   $118.95   $119.00  
  7 purchase totals = $1,154.68       $1,274.5667   $1,274.56   $1,274.60   $1,274.60