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 $228.73   5.527%   $241.3719   $241.37   $241.35   $241.40  
  Purchase #2 $139.49   9.649%   $152.9494   $152.95   $152.95   $152.90  
  Purchase #3 $127.63   13.214%   $144.495   $144.50   $144.50   $144.50  
  Purchase #4 $167.45   8.123%   $181.052   $181.05   $181.05   $181.10  
  Purchase #5 $236.30   13.812%   $268.9378   $268.94   $268.95   $268.90  
  Purchase #6 $120.39   3.387%   $124.4676   $124.47   $124.45   $124.50  
  Purchase #7 $115.71   3.489%   $119.7471   $119.75   $119.75   $119.70  
  7 purchase totals = $1,135.70       $1,233.0208   $1,233.03   $1,233.00   $1,233.00