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 $215.71   12.263%   $242.1625   $242.16   $242.15   $242.20  
  Purchase #2 $38.48   8.107%   $41.5996   $41.60   $41.60   $41.60  
  Purchase #3 $113.77   10.685%   $125.9263   $125.93   $125.95   $125.90  
  Purchase #4 $43.51   10.177%   $47.938   $47.94   $47.95   $47.90  
  Purchase #5 $130.42   5.619%   $137.7483   $137.75   $137.75   $137.70  
  Purchase #6 $137.93   6.512%   $146.912   $146.91   $146.90   $146.90  
  Purchase #7 $247.89   10.540%   $274.0176   $274.02   $274.00   $274.00  
  7 purchase totals = $927.71       $1,016.3043   $1,016.31   $1,016.30   $1,016.20