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 $243.78   4.828%   $255.5497   $255.55   $255.55   $255.50  
  Purchase #2 $246.85   11.353%   $274.8749   $274.87   $274.85   $274.90  
  Purchase #3 $234.78   13.873%   $267.351   $267.35   $267.35   $267.40  
  Purchase #4 $157.88   11.199%   $175.561   $175.56   $175.55   $175.60  
  Purchase #5 $181.99   9.694%   $199.6321   $199.63   $199.65   $199.60  
  Purchase #6 $233.56   12.165%   $261.9726   $261.97   $261.95   $262.00  
  Purchase #7 $29.69   4.551%   $31.0412   $31.04   $31.05   $31.00  
  7 purchase totals = $1,328.53       $1,465.9825   $1,465.97   $1,465.95   $1,466.00