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 $164.92   10.752%   $182.6522   $182.65   $182.65   $182.70  
  Purchase #2 $248.59   10.339%   $274.2917   $274.29   $274.30   $274.30  
  Purchase #3 $169.47   12.455%   $190.5775   $190.58   $190.60   $190.60  
  Purchase #4 $217.89   12.428%   $244.9694   $244.97   $244.95   $245.00  
  Purchase #5 $26.49   11.693%   $29.5875   $29.59   $29.60   $29.60  
  Purchase #6 $242.93   9.213%   $265.3111   $265.31   $265.30   $265.30  
  Purchase #7 $234.97   6.129%   $249.3713   $249.37   $249.35   $249.40  
  7 purchase totals = $1,305.26       $1,436.7607   $1,436.76   $1,436.75   $1,436.90