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 $214.94   12.834%   $242.5254   $242.53   $242.55   $242.50  
  Purchase #2 $22.59   4.341%   $23.5706   $23.57   $23.55   $23.60  
  Purchase #3 $61.55   8.155%   $66.5694   $66.57   $66.55   $66.60  
  Purchase #4 $116.77   7.261%   $125.2487   $125.25   $125.25   $125.20  
  Purchase #5 $73.70   4.546%   $77.0504   $77.05   $77.05   $77.10  
  Purchase #6 $237.59   4.287%   $247.7755   $247.78   $247.80   $247.80  
  Purchase #7 $247.92   4.639%   $259.421   $259.42   $259.40   $259.40  
  7 purchase totals = $975.06       $1,042.1610   $1,042.17   $1,042.15   $1,042.20