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 $239.54   5.572%   $252.8872   $252.89   $252.90   $252.90  
  Purchase #2 $233.31   12.163%   $261.6875   $261.69   $261.70   $261.70  
  Purchase #3 $111.53   4.385%   $116.4206   $116.42   $116.40   $116.40  
  Purchase #4 $221.64   6.673%   $236.43   $236.43   $236.45   $236.40  
  Purchase #5 $195.58   12.760%   $220.536   $220.54   $220.55   $220.50  
  Purchase #6 $155.45   8.444%   $168.5762   $168.58   $168.60   $168.60  
  Purchase #7 $18.76   8.256%   $20.3088   $20.31   $20.30   $20.30  
  7 purchase totals = $1,175.81       $1,276.8463   $1,276.86   $1,276.90   $1,276.80