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 $63.82   10.733%   $70.6698   $70.67   $70.65   $70.70  
  Purchase #2 $73.54   6.291%   $78.1664   $78.17   $78.15   $78.20  
  Purchase #3 $227.67   3.594%   $235.8525   $235.85   $235.85   $235.90  
  Purchase #4 $107.37   8.497%   $116.4932   $116.49   $116.50   $116.50  
  Purchase #5 $71.91   6.858%   $76.8416   $76.84   $76.85   $76.80  
  Purchase #6 $233.87   5.386%   $246.4662   $246.47   $246.45   $246.50  
  Purchase #7 $30.56   12.546%   $34.3941   $34.39   $34.40   $34.40  
  7 purchase totals = $808.74       $858.8838   $858.88   $858.85   $859.00