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	$19.54	10.516%	$21.5948	$21.59	$21.60	$21.60
Purchase #2	$33.91	11.713%	$37.8819	$37.88	$37.90	$37.90
Purchase #3	$192.83	11.699%	$215.3892	$215.39	$215.40	$215.40
Purchase #4	$157.65	7.661%	$169.7276	$169.73	$169.75	$169.70
Purchase #5	$67.32	6.336%	$71.5854	$71.59	$71.60	$71.60
Purchase #6	$121.68	10.431%	$134.3724	$134.37	$134.35	$134.40
Purchase #7	$103.62	8.558%	$112.4878	$112.49	$112.50	$112.50
7 purchase totals =	$696.55		$763.0391	$763.04	$763.10	$763.10