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 $240.58   7.628%   $258.9314   $258.93   $258.95   $258.90  
  Purchase #2 $148.43   7.565%   $159.6587   $159.66   $159.65   $159.70  
  Purchase #3 $247.54   7.520%   $266.155   $266.16   $266.15   $266.20  
  Purchase #4 $226.29   4.412%   $236.2739   $236.27   $236.25   $236.30  
  Purchase #5 $67.28   10.294%   $74.2058   $74.21   $74.20   $74.20  
  Purchase #6 $131.86   6.177%   $140.005   $140.01   $140.00   $140.00  
  Purchase #7 $247.40   12.162%   $277.4888   $277.49   $277.50   $277.50  
  7 purchase totals = $1,309.38       $1,412.7186   $1,412.73   $1,412.70   $1,412.80