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 $185.98   10.597%   $205.6883   $205.69   $205.70   $205.70  
  Purchase #2 $60.25   3.398%   $62.2973   $62.30   $62.30   $62.30  
  Purchase #3 $67.89   5.461%   $71.5975   $71.60   $71.60   $71.60  
  Purchase #4 $66.98   13.763%   $76.1985   $76.20   $76.20   $76.20  
  Purchase #5 $222.39   4.372%   $232.1129   $232.11   $232.10   $232.10  
  Purchase #6 $110.60   7.788%   $119.2135   $119.21   $119.20   $119.20  
  Purchase #7 $142.67   11.547%   $159.1441   $159.14   $159.15   $159.10  
  7 purchase totals = $856.76       $926.2521   $926.25   $926.25   $926.20