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 $60.96   9.187%   $66.5604   $66.56   $66.55   $66.60  
  Purchase #2 $234.65   11.384%   $261.3626   $261.36   $261.35   $261.40  
  Purchase #3 $195.27   6.152%   $207.283   $207.28   $207.30   $207.30  
  Purchase #4 $125.70   13.208%   $142.3025   $142.30   $142.30   $142.30  
  Purchase #5 $146.41   11.135%   $162.7128   $162.71   $162.70   $162.70  
  Purchase #6 $194.45   4.482%   $203.1652   $203.17   $203.15   $203.20  
  Purchase #7 $229.56   11.242%   $255.3671   $255.37   $255.35   $255.40  
  7 purchase totals = $1,187.00       $1,298.7536   $1,298.75   $1,298.70   $1,298.90