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 $246.90   5.788%   $261.1906   $261.19   $261.20   $261.20  
  Purchase #2 $123.67   5.148%   $130.0365   $130.04   $130.05   $130.00  
  Purchase #3 $118.31   5.223%   $124.4893   $124.49   $124.50   $124.50  
  Purchase #4 $163.46   12.609%   $184.0707   $184.07   $184.05   $184.10  
  Purchase #5 $5.90   6.274%   $6.2702   $6.27   $6.25   $6.30  
  Purchase #6 $100.62   3.353%   $103.9938   $103.99   $104.00   $104.00  
  Purchase #7 $15.46   5.293%   $16.2783   $16.28   $16.30   $16.30  
  7 purchase totals = $774.32       $826.3294   $826.33   $826.35   $826.40