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 $96.39   13.291%   $109.2012   $109.20   $109.20   $109.20  
  Purchase #2 $217.61   6.660%   $232.1028   $232.10   $232.10   $232.10  
  Purchase #3 $40.74   9.376%   $44.5598   $44.56   $44.55   $44.60  
  Purchase #4 $71.57   4.269%   $74.6253   $74.63   $74.65   $74.60  
  Purchase #5 $68.91   3.244%   $71.1454   $71.15   $71.15   $71.10  
  Purchase #6 $215.46   10.369%   $237.801   $237.80   $237.80   $237.80  
  Purchase #7 $241.62   5.573%   $255.0855   $255.09   $255.10   $255.10  
  7 purchase totals = $952.30       $1,024.5210   $1,024.53   $1,024.55   $1,024.50