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 $202.95   6.514%   $216.1702   $216.17   $216.15   $216.20  
  Purchase #2 $199.65   9.597%   $218.8104   $218.81   $218.80   $218.80  
  Purchase #3 $70.66   4.613%   $73.9195   $73.92   $73.90   $73.90  
  Purchase #4 $23.28   9.285%   $25.4415   $25.44   $25.45   $25.40  
  Purchase #5 $214.95   11.169%   $238.9578   $238.96   $238.95   $239.00  
  Purchase #6 $236.53   10.713%   $261.8695   $261.87   $261.85   $261.90  
  Purchase #7 $7.50   5.775%   $7.9331   $7.93   $7.95   $7.90  
  7 purchase totals = $955.52       $1,043.1020   $1,043.10   $1,043.05   $1,043.10