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	$247.84	3.532%	$256.5937	$256.59	$256.60	$256.60
Purchase #2	$113.36	12.442%	$127.4643	$127.46	$127.45	$127.50
Purchase #3	$75.77	8.773%	$82.4173	$82.42	$82.40	$82.40
Purchase #4	$31.87	5.343%	$33.5728	$33.57	$33.55	$33.60
Purchase #5	$192.85	9.557%	$211.2807	$211.28	$211.30	$211.30
Purchase #6	$84.67	5.634%	$89.4403	$89.44	$89.45	$89.40
Purchase #7	$42.76	6.134%	$45.3829	$45.38	$45.40	$45.40
7 purchase totals =	$789.12		$846.1520	$846.14	$846.15	$846.20