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 $233.53   8.307%   $252.9293   $252.93   $252.95   $252.90  
  Purchase #2 $199.96   7.693%   $215.3429   $215.34   $215.35   $215.30  
  Purchase #3 $205.47   13.863%   $233.9543   $233.95   $233.95   $234.00  
  Purchase #4 $144.50   9.154%   $157.7275   $157.73   $157.75   $157.70  
  Purchase #5 $231.95   7.381%   $249.0702   $249.07   $249.05   $249.10  
  Purchase #6 $110.86   12.609%   $124.8383   $124.84   $124.85   $124.80  
  Purchase #7 $25.94   7.612%   $27.9146   $27.91   $27.90   $27.90  
  7 purchase totals = $1,152.21       $1,261.7771   $1,261.77   $1,261.80   $1,261.70