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 $101.45   9.444%   $111.0309   $111.03   $111.05   $111.00  
  Purchase #2 $153.38   6.231%   $162.9371   $162.94   $162.95   $162.90  
  Purchase #3 $226.97   9.465%   $248.4527   $248.45   $248.45   $248.50  
  Purchase #4 $233.43   10.215%   $257.2749   $257.27   $257.25   $257.30  
  Purchase #5 $126.76   11.465%   $141.293   $141.29   $141.30   $141.30  
  Purchase #6 $20.47   11.373%   $22.7981   $22.80   $22.80   $22.80  
  Purchase #7 $160.92   9.503%   $176.2122   $176.21   $176.20   $176.20  
  7 purchase totals = $1,023.38       $1,119.9989   $1,119.99   $1,120.00   $1,120.00