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 $216.60   13.564%   $245.9796   $245.98   $246.00   $246.00  
  Purchase #2 $75.46   5.562%   $79.6571   $79.66   $79.65   $79.70  
  Purchase #3 $123.63   12.836%   $139.4991   $139.50   $139.50   $139.50  
  Purchase #4 $232.37   7.437%   $249.6514   $249.65   $249.65   $249.70  
  Purchase #5 $112.75   13.141%   $127.5665   $127.57   $127.55   $127.60  
  Purchase #6 $89.66   12.790%   $101.1275   $101.13   $101.15   $101.10  
  Purchase #7 $161.76   5.401%   $170.4967   $170.50   $170.50   $170.50  
  7 purchase totals = $1,012.23       $1,113.9779   $1,113.99   $1,114.00   $1,114.10