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 $60.87   7.142%   $65.2173   $65.22   $65.20   $65.20  
  Purchase #2 $242.55   4.316%   $253.0185   $253.02   $253.00   $253.00  
  Purchase #3 $28.36   11.804%   $31.7076   $31.71   $31.70   $31.70  
  Purchase #4 $68.47   11.833%   $76.5721   $76.57   $76.55   $76.60  
  Purchase #5 $183.97   12.302%   $206.602   $206.60   $206.60   $206.60  
  Purchase #6 $232.28   9.826%   $255.1038   $255.10   $255.10   $255.10  
  Purchase #7 $219.86   5.394%   $231.7192   $231.72   $231.70   $231.70  
  7 purchase totals = $1,036.36       $1,119.9405   $1,119.94   $1,119.85   $1,119.90