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	$162.59	4.559%	$170.0025	$170.00	$170.00	$170.00
Purchase #2	$142.52	8.120%	$154.0926	$154.09	$154.10	$154.10
Purchase #3	$111.76	10.146%	$123.0992	$123.10	$123.10	$123.10
Purchase #4	$83.52	11.463%	$93.0939	$93.09	$93.10	$93.10
Purchase #5	$112.71	13.465%	$127.8864	$127.89	$127.90	$127.90
Purchase #6	$241.44	7.576%	$259.7315	$259.73	$259.75	$259.70
Purchase #7	$73.71	7.594%	$79.3075	$79.31	$79.30	$79.30
7 purchase totals =	$928.25		$1,007.2136	$1,007.21	$1,007.25	$1,007.20