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	$77.71	7.655%	$83.6587	$83.66	$83.65	$83.70
Purchase #2	$250.94	10.831%	$278.1193	$278.12	$278.10	$278.10
Purchase #3	$50.92	4.355%	$53.1376	$53.14	$53.15	$53.10
Purchase #4	$135.68	12.619%	$152.8015	$152.80	$152.80	$152.80
Purchase #5	$143.60	13.262%	$162.6442	$162.64	$162.65	$162.60
Purchase #6	$97.89	8.194%	$105.9111	$105.91	$105.90	$105.90
Purchase #7	$84.31	5.773%	$89.1772	$89.18	$89.20	$89.20
7 purchase totals =	$841.05		$925.4496	$925.45	$925.45	$925.40