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 $14.93   13.272%   $16.9115   $16.91   $16.90   $16.90  
  Purchase #2 $226.91   10.592%   $250.9443   $250.94   $250.95   $250.90  
  Purchase #3 $248.86   7.515%   $267.5618   $267.56   $267.55   $267.60  
  Purchase #4 $15.70   5.135%   $16.5062   $16.51   $16.50   $16.50  
  Purchase #5 $233.78   6.229%   $248.3422   $248.34   $248.35   $248.30  
  Purchase #6 $155.43   7.561%   $167.1821   $167.18   $167.20   $167.20  
  Purchase #7 $186.29   11.859%   $208.3821   $208.38   $208.40   $208.40  
  7 purchase totals = $1,081.90       $1,175.8302   $1,175.82   $1,175.85   $1,175.80