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 $216.53   8.618%   $235.1906   $235.19   $235.20   $235.20  
  Purchase #2 $182.87   7.447%   $196.4883   $196.49   $196.50   $196.50  
  Purchase #3 $40.90   7.610%   $44.0125   $44.01   $44.00   $44.00  
  Purchase #4 $230.73   9.646%   $252.9862   $252.99   $253.00   $253.00  
  Purchase #5 $90.75   7.480%   $97.5381   $97.54   $97.55   $97.50  
  Purchase #6 $175.61   6.178%   $186.4592   $186.46   $186.45   $186.50  
  Purchase #7 $217.49   5.669%   $229.8195   $229.82   $229.80   $229.80  
  7 purchase totals = $1,154.88       $1,242.4944   $1,242.50   $1,242.50   $1,242.50