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	$145.58	13.757%	$165.6074	$165.61	$165.60	$165.60
Purchase #2	$61.79	11.250%	$68.7414	$68.74	$68.75	$68.70
Purchase #3	$38.49	13.796%	$43.8001	$43.80	$43.80	$43.80
Purchase #4	$94.50	5.499%	$99.6966	$99.70	$99.70	$99.70
Purchase #5	$31.99	9.581%	$35.055	$35.06	$35.05	$35.10
Purchase #6	$98.83	11.430%	$110.1263	$110.13	$110.15	$110.10
Purchase #7	$116.51	5.770%	$123.2326	$123.23	$123.25	$123.20
7 purchase totals =	$587.69		$646.2594	$646.27	$646.30	$646.20