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	$54.45	8.557%	$59.1093	$59.11	$59.10	$59.10
Purchase #2	$30.35	10.235%	$33.4563	$33.46	$33.45	$33.50
Purchase #3	$68.52	9.690%	$75.1596	$75.16	$75.15	$75.20
Purchase #4	$116.64	6.169%	$123.8355	$123.84	$123.85	$123.80
Purchase #5	$237.34	13.534%	$269.4616	$269.46	$269.45	$269.50
Purchase #6	$184.98	11.749%	$206.7133	$206.71	$206.70	$206.70
Purchase #7	$98.55	13.247%	$111.6049	$111.60	$111.60	$111.60
7 purchase totals =	$790.83		$879.3405	$879.34	$879.30	$879.40