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 $57.26   10.136%   $63.0639   $63.06   $63.05   $63.10  
  Purchase #2 $204.89   12.207%   $229.9009   $229.90   $229.90   $229.90  
  Purchase #3 $214.66   12.759%   $242.0485   $242.05   $242.05   $242.00  
  Purchase #4 $121.34   12.315%   $136.283   $136.28   $136.30   $136.30  
  Purchase #5 $214.72   10.660%   $237.6092   $237.61   $237.60   $237.60  
  Purchase #6 $234.34   11.594%   $261.5094   $261.51   $261.50   $261.50  
  Purchase #7 $63.51   4.570%   $66.4124   $66.41   $66.40   $66.40  
  7 purchase totals = $1,110.72       $1,236.8273   $1,236.82   $1,236.80   $1,236.80