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 $227.25   6.287%   $241.5372   $241.54   $241.55   $241.50  
  Purchase #2 $215.97   10.853%   $239.4092   $239.41   $239.40   $239.40  
  Purchase #3 $173.63   5.317%   $182.8619   $182.86   $182.85   $182.90  
  Purchase #4 $233.63   12.578%   $263.016   $263.02   $263.00   $263.00  
  Purchase #5 $76.34   8.818%   $83.0717   $83.07   $83.05   $83.10  
  Purchase #6 $170.65   5.642%   $180.2781   $180.28   $180.30   $180.30  
  Purchase #7 $244.51   3.614%   $253.3466   $253.35   $253.35   $253.30  
  7 purchase totals = $1,341.98       $1,443.5207   $1,443.53   $1,443.50   $1,443.50