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 $236.84   11.539%   $264.169   $264.17   $264.15   $264.20  
  Purchase #2 $23.68   4.506%   $24.747   $24.75   $24.75   $24.70  
  Purchase #3 $129.48   10.252%   $142.7543   $142.75   $142.75   $142.80  
  Purchase #4 $238.61   10.514%   $263.6975   $263.70   $263.70   $263.70  
  Purchase #5 $247.90   5.476%   $261.475   $261.48   $261.50   $261.50  
  Purchase #6 $95.72   5.826%   $101.2966   $101.30   $101.30   $101.30  
  Purchase #7 $178.83   12.644%   $201.4413   $201.44   $201.45   $201.40  
  7 purchase totals = $1,151.06       $1,259.5807   $1,259.59   $1,259.60   $1,259.60