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 $213.92   12.805%   $241.3125   $241.31   $241.30   $241.30  
  Purchase #2 $132.63   10.682%   $146.7975   $146.80   $146.80   $146.80  
  Purchase #3 $55.36   6.479%   $58.9468   $58.95   $58.95   $58.90  
  Purchase #4 $176.54   13.649%   $200.6359   $200.64   $200.65   $200.60  
  Purchase #5 $62.72   5.469%   $66.1502   $66.15   $66.15   $66.20  
  Purchase #6 $40.84   6.269%   $43.4003   $43.40   $43.40   $43.40  
  Purchase #7 $108.94   7.776%   $117.4112   $117.41   $117.40   $117.40  
  7 purchase totals = $790.95       $874.6544   $874.66   $874.65   $874.60