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 $246.41   9.210%   $269.1044   $269.10   $269.10   $269.10  
  Purchase #2 $238.94   9.553%   $261.7659   $261.77   $261.75   $261.80  
  Purchase #3 $64.93   3.728%   $67.3506   $67.35   $67.35   $67.40  
  Purchase #4 $66.97   10.272%   $73.8492   $73.85   $73.85   $73.80  
  Purchase #5 $245.46   13.790%   $279.3089   $279.31   $279.30   $279.30  
  Purchase #6 $114.37   10.495%   $126.3731   $126.37   $126.35   $126.40  
  Purchase #7 $83.80   11.722%   $93.623   $93.62   $93.60   $93.60  
  7 purchase totals = $1,060.88       $1,171.3751   $1,171.37   $1,171.30   $1,171.40