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 $180.51   6.873%   $192.9165   $192.92   $192.90   $192.90  
  Purchase #2 $245.92   11.418%   $273.9991   $274.00   $274.00   $274.00  
  Purchase #3 $71.31   3.727%   $73.9677   $73.97   $73.95   $74.00  
  Purchase #4 $18.58   6.128%   $19.7186   $19.72   $19.70   $19.70  
  Purchase #5 $122.63   5.419%   $129.2753   $129.28   $129.30   $129.30  
  Purchase #6 $15.26   5.481%   $16.0964   $16.10   $16.10   $16.10  
  Purchase #7 $224.33   11.285%   $249.6456   $249.65   $249.65   $249.60  
  7 purchase totals = $878.54       $955.6192   $955.64   $955.60   $955.60