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	$19.36	11.788%	$21.6422	$21.64	$21.65	$21.60
Purchase #2	$121.53	8.494%	$131.8528	$131.85	$131.85	$131.90
Purchase #3	$83.82	8.449%	$90.902	$90.90	$90.90	$90.90
Purchase #4	$14.91	13.598%	$16.9375	$16.94	$16.95	$16.90
Purchase #5	$235.59	6.275%	$250.3733	$250.37	$250.35	$250.40
Purchase #6	$130.87	10.755%	$144.9451	$144.95	$144.95	$144.90
Purchase #7	$209.81	3.428%	$217.0023	$217.00	$217.00	$217.00
7 purchase totals =	$815.89		$873.6552	$873.65	$873.65	$873.60