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 $81.29   13.544%   $92.2999   $92.30   $92.30   $92.30  
  Purchase #2 $197.81   7.118%   $211.8901   $211.89   $211.90   $211.90  
  Purchase #3 $46.77   11.729%   $52.2557   $52.26   $52.25   $52.30  
  Purchase #4 $249.74   4.520%   $261.0282   $261.03   $261.05   $261.00  
  Purchase #5 $231.75   3.326%   $239.458   $239.46   $239.45   $239.50  
  Purchase #6 $23.40   6.466%   $24.913   $24.91   $24.90   $24.90  
  Purchase #7 $132.65   6.560%   $141.3518   $141.35   $141.35   $141.40  
  7 purchase totals = $963.41       $1,023.1967   $1,023.20   $1,023.20   $1,023.30