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 $213.71   13.453%   $242.4604   $242.46   $242.45   $242.50  
  Purchase #2 $167.39   5.567%   $176.7086   $176.71   $176.70   $176.70  
  Purchase #3 $118.49   13.492%   $134.4767   $134.48   $134.50   $134.50  
  Purchase #4 $183.31   3.230%   $189.2309   $189.23   $189.25   $189.20  
  Purchase #5 $48.25   5.492%   $50.8999   $50.90   $50.90   $50.90  
  Purchase #6 $121.54   6.366%   $129.2772   $129.28   $129.30   $129.30  
  Purchase #7 $87.34   10.602%   $96.5998   $96.60   $96.60   $96.60  
  7 purchase totals = $940.03       $1,019.6535   $1,019.66   $1,019.70   $1,019.70