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	$147.63	7.121%	$158.1427	$158.14	$158.15	$158.10
Purchase #2	$50.27	11.716%	$56.1596	$56.16	$56.15	$56.20
Purchase #3	$204.25	5.465%	$215.4123	$215.41	$215.40	$215.40
Purchase #4	$40.88	11.714%	$45.6687	$45.67	$45.65	$45.70
Purchase #5	$210.50	10.576%	$232.7625	$232.76	$232.75	$232.80
Purchase #6	$111.79	10.560%	$123.595	$123.60	$123.60	$123.60
Purchase #7	$62.86	6.231%	$66.7768	$66.78	$66.80	$66.80
7 purchase totals =	$828.18		$898.5176	$898.52	$898.50	$898.60