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 $59.32   13.136%   $67.1123   $67.11   $67.10   $67.10  
  Purchase #2 $144.85   9.621%   $158.786   $158.79   $158.80   $158.80  
  Purchase #3 $14.40   4.418%   $15.0362   $15.04   $15.05   $15.00  
  Purchase #4 $75.85   13.688%   $86.2323   $86.23   $86.25   $86.20  
  Purchase #5 $241.71   13.359%   $274   $274.00   $274.00   $274.00  
  Purchase #6 $92.63   4.156%   $96.4797   $96.48   $96.50   $96.50  
  Purchase #7 $218.73   12.493%   $246.0559   $246.06   $246.05   $246.10  
  7 purchase totals = $847.49       $943.7024   $943.71   $943.75   $943.70