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 $244.83   6.622%   $261.0426   $261.04   $261.05   $261.00  
  Purchase #2 $198.98   6.540%   $211.9933   $211.99   $212.00   $212.00  
  Purchase #3 $114.61   4.853%   $120.172   $120.17   $120.15   $120.20  
  Purchase #4 $66.61   11.339%   $74.1629   $74.16   $74.15   $74.20  
  Purchase #5 $22.74   8.268%   $24.6201   $24.62   $24.60   $24.60  
  Purchase #6 $20.49   9.708%   $22.4792   $22.48   $22.50   $22.50  
  Purchase #7 $90.45   6.698%   $96.5083   $96.51   $96.50   $96.50  
  7 purchase totals = $758.71       $810.9784   $810.97   $810.95   $811.00