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 $87.38   6.824%   $93.3428   $93.34   $93.35   $93.30  
  Purchase #2 $195.73   8.286%   $211.9482   $211.95   $211.95   $211.90  
  Purchase #3 $142.99   3.839%   $148.4794   $148.48   $148.50   $148.50  
  Purchase #4 $202.42   12.509%   $227.7407   $227.74   $227.75   $227.70  
  Purchase #5 $248.82   3.762%   $258.1806   $258.18   $258.20   $258.20  
  Purchase #6 $75.94   5.181%   $79.8745   $79.87   $79.85   $79.90  
  Purchase #7 $5.86   13.676%   $6.6614   $6.66   $6.65   $6.70  
  7 purchase totals = $959.14       $1,026.2276   $1,026.22   $1,026.25   $1,026.20