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 $62.84   6.647%   $67.017   $67.02   $67.00   $67.00  
  Purchase #2 $21.49   7.510%   $23.1039   $23.10   $23.10   $23.10  
  Purchase #3 $171.27   4.135%   $178.352   $178.35   $178.35   $178.40  
  Purchase #4 $192.77   8.183%   $208.5444   $208.54   $208.55   $208.50  
  Purchase #5 $38.76   11.586%   $43.2507   $43.25   $43.25   $43.30  
  Purchase #6 $173.42   5.327%   $182.6581   $182.66   $182.65   $182.70  
  Purchase #7 $161.65   7.658%   $174.0292   $174.03   $174.05   $174.00  
  7 purchase totals = $822.20       $876.9553   $876.95   $876.95   $877.00