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 $64.47   11.110%   $71.6326   $71.63   $71.65   $71.60  
  Purchase #2 $124.88   4.227%   $130.1587   $130.16   $130.15   $130.20  
  Purchase #3 $217.54   4.119%   $226.5005   $226.50   $226.50   $226.50  
  Purchase #4 $137.53   6.676%   $146.7115   $146.71   $146.70   $146.70  
  Purchase #5 $106.72   7.195%   $114.3985   $114.40   $114.40   $114.40  
  Purchase #6 $208.88   9.735%   $229.2145   $229.21   $229.20   $229.20  
  Purchase #7 $122.46   9.350%   $133.91   $133.91   $133.90   $133.90  
  7 purchase totals = $982.48       $1,052.5263   $1,052.52   $1,052.50   $1,052.50