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 $247.70   5.709%   $261.8412   $261.84   $261.85   $261.80  
  Purchase #2 $214.93   3.775%   $223.0436   $223.04   $223.05   $223.00  
  Purchase #3 $52.69   6.528%   $56.1296   $56.13   $56.15   $56.10  
  Purchase #4 $174.72   11.698%   $195.1587   $195.16   $195.15   $195.20  
  Purchase #5 $230.45   4.757%   $241.4125   $241.41   $241.40   $241.40  
  Purchase #6 $46.96   8.522%   $50.9619   $50.96   $50.95   $51.00  
  Purchase #7 $60.50   7.772%   $65.2021   $65.20   $65.20   $65.20  
  7 purchase totals = $1,027.95       $1,093.7496   $1,093.74   $1,093.75   $1,093.70