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 $89.84   9.777%   $98.6237   $98.62   $98.60   $98.60  
  Purchase #2 $124.91   11.711%   $139.5382   $139.54   $139.55   $139.50  
  Purchase #3 $195.53   9.494%   $214.0936   $214.09   $214.10   $214.10  
  Purchase #4 $138.83   5.676%   $146.71   $146.71   $146.70   $146.70  
  Purchase #5 $214.61   8.435%   $232.7124   $232.71   $232.70   $232.70  
  Purchase #6 $90.30   8.756%   $98.2067   $98.21   $98.20   $98.20  
  Purchase #7 $87.65   5.752%   $92.6916   $92.69   $92.70   $92.70  
  7 purchase totals = $941.67       $1,022.5762   $1,022.57   $1,022.55   $1,022.50