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 $57.61   9.653%   $63.1711   $63.17   $63.15   $63.20  
  Purchase #2 $240.99   10.392%   $266.0337   $266.03   $266.05   $266.00  
  Purchase #3 $246.30   6.166%   $261.4869   $261.49   $261.50   $261.50  
  Purchase #4 $32.29   12.249%   $36.2452   $36.25   $36.25   $36.20  
  Purchase #5 $74.88   11.439%   $83.4455   $83.45   $83.45   $83.40  
  Purchase #6 $40.63   10.142%   $44.7507   $44.75   $44.75   $44.80  
  Purchase #7 $79.83   12.828%   $90.0706   $90.07   $90.05   $90.10  
  7 purchase totals = $772.53       $845.2037   $845.21   $845.20   $845.20