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 $60.90   13.287%   $68.9918   $68.99   $69.00   $69.00  
  Purchase #2 $230.92   13.226%   $261.4615   $261.46   $261.45   $261.50  
  Purchase #3 $218.97   10.492%   $241.9443   $241.94   $241.95   $241.90  
  Purchase #4 $103.47   12.770%   $116.6831   $116.68   $116.70   $116.70  
  Purchase #5 $130.30   7.668%   $140.2914   $140.29   $140.30   $140.30  
  Purchase #6 $20.74   3.671%   $21.5014   $21.50   $21.50   $21.50  
  Purchase #7 $172.26   6.260%   $183.0435   $183.04   $183.05   $183.00  
  7 purchase totals = $937.56       $1,033.9170   $1,033.90   $1,033.95   $1,033.90