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	$202.34	8.663%	$219.8687	$219.87	$219.85	$219.90
Purchase #2	$143.29	7.859%	$154.5512	$154.55	$154.55	$154.60
Purchase #3	$131.86	11.321%	$146.7879	$146.79	$146.80	$146.80
Purchase #4	$134.66	4.862%	$141.2072	$141.21	$141.20	$141.20
Purchase #5	$64.69	4.704%	$67.733	$67.73	$67.75	$67.70
Purchase #6	$53.56	12.315%	$60.1559	$60.16	$60.15	$60.20
Purchase #7	$182.67	3.149%	$188.4223	$188.42	$188.40	$188.40
7 purchase totals =	$913.07		$978.7262	$978.73	$978.70	$978.80