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	$155.76	3.795%	$161.6711	$161.67	$161.65	$161.70
Purchase #2	$47.71	11.671%	$53.2782	$53.28	$53.30	$53.30
Purchase #3	$230.87	3.336%	$238.5718	$238.57	$238.55	$238.60
Purchase #4	$79.28	12.420%	$89.1266	$89.13	$89.15	$89.10
Purchase #5	$8.36	13.395%	$9.4798	$9.48	$9.50	$9.50
Purchase #6	$87.90	13.840%	$100.0654	$100.07	$100.05	$100.10
Purchase #7	$12.55	8.430%	$13.608	$13.61	$13.60	$13.60
7 purchase totals =	$622.43		$665.8009	$665.81	$665.80	$665.90