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 $40.82   6.102%   $43.3108   $43.31   $43.30   $43.30  
  Purchase #2 $172.26   13.136%   $194.8881   $194.89   $194.90   $194.90  
  Purchase #3 $188.38   9.635%   $206.5304   $206.53   $206.55   $206.50  
  Purchase #4 $79.32   13.523%   $90.0464   $90.05   $90.05   $90.00  
  Purchase #5 $216.68   5.106%   $227.7437   $227.74   $227.75   $227.70  
  Purchase #6 $175.57   7.311%   $188.4059   $188.41   $188.40   $188.40  
  Purchase #7 $108.65   9.536%   $119.0109   $119.01   $119.00   $119.00  
  7 purchase totals = $981.68       $1,069.9362   $1,069.94   $1,069.95   $1,069.80