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	$192.51	11.323%	$214.3079	$214.31	$214.30	$214.30
Purchase #2	$202.87	11.293%	$225.7801	$225.78	$225.80	$225.80
Purchase #3	$132.31	5.629%	$139.7577	$139.76	$139.75	$139.80
Purchase #4	$129.95	10.165%	$143.1594	$143.16	$143.15	$143.20
Purchase #5	$143.42	3.487%	$148.4211	$148.42	$148.40	$148.40
Purchase #6	$111.79	4.470%	$116.787	$116.79	$116.80	$116.80
Purchase #7	$128.91	11.330%	$143.5155	$143.52	$143.50	$143.50
7 purchase totals =	$1,041.76		$1,131.7287	$1,131.74	$1,131.70	$1,131.80