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 $96.76   4.165%   $100.7901   $100.79   $100.80   $100.80  
  Purchase #2 $150.92   4.251%   $157.3356   $157.34   $157.35   $157.30  
  Purchase #3 $123.48   8.860%   $134.4203   $134.42   $134.40   $134.40  
  Purchase #4 $69.63   10.411%   $76.8792   $76.88   $76.90   $76.90  
  Purchase #5 $96.32   3.794%   $99.9744   $99.97   $99.95   $100.00  
  Purchase #6 $207.91   3.825%   $215.8626   $215.86   $215.85   $215.90  
  Purchase #7 $89.68   7.214%   $96.1495   $96.15   $96.15   $96.10  
  7 purchase totals = $834.70       $881.4117   $881.41   $881.40   $881.40