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	$76.90	7.832%	$82.9228	$82.92	$82.90	$82.90
Purchase #2	$57.73	4.166%	$60.135	$60.14	$60.15	$60.10
Purchase #3	$129.45	10.369%	$142.8727	$142.87	$142.85	$142.90
Purchase #4	$238.45	6.168%	$253.1576	$253.16	$253.15	$253.20
Purchase #5	$116.65	13.510%	$132.4094	$132.41	$132.40	$132.40
Purchase #6	$153.81	12.333%	$172.7794	$172.78	$172.80	$172.80
Purchase #7	$206.50	7.757%	$222.5182	$222.52	$222.50	$222.50
7 purchase totals =	$979.49		$1,066.7951	$1,066.80	$1,066.75	$1,066.80