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 $235.84   4.108%   $245.5283   $245.53   $245.55   $245.50  
  Purchase #2 $207.99   9.429%   $227.6014   $227.60   $227.60   $227.60  
  Purchase #3 $66.70   7.489%   $71.6952   $71.70   $71.70   $71.70  
  Purchase #4 $19.66   12.600%   $22.1372   $22.14   $22.15   $22.10  
  Purchase #5 $92.88   3.357%   $95.998   $96.00   $96.00   $96.00  
  Purchase #6 $202.28   6.284%   $214.9913   $214.99   $215.00   $215.00  
  Purchase #7 $106.61   11.781%   $119.1697   $119.17   $119.15   $119.20  
  7 purchase totals = $931.96       $997.1211   $997.13   $997.15   $997.10