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 $192.79   8.571%   $209.314   $209.31   $209.30   $209.30  
  Purchase #2 $240.25   9.199%   $262.3506   $262.35   $262.35   $262.40  
  Purchase #3 $153.83   5.449%   $162.2122   $162.21   $162.20   $162.20  
  Purchase #4 $69.30   4.312%   $72.2882   $72.29   $72.30   $72.30  
  Purchase #5 $196.58   12.138%   $220.4409   $220.44   $220.45   $220.40  
  Purchase #6 $176.33   7.522%   $189.5935   $189.59   $189.60   $189.60  
  Purchase #7 $133.94   6.739%   $142.9662   $142.97   $142.95   $143.00  
  7 purchase totals = $1,163.02       $1,259.1656   $1,259.16   $1,259.15   $1,259.20