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	$51.29	10.373%	$56.6103	$56.61	$56.60	$56.60
Purchase #2	$78.27	5.845%	$82.8449	$82.84	$82.85	$82.80
Purchase #3	$48.41	4.707%	$50.6887	$50.69	$50.70	$50.70
Purchase #4	$89.51	7.553%	$96.2707	$96.27	$96.25	$96.30
Purchase #5	$139.98	4.690%	$146.5451	$146.55	$146.55	$146.50
Purchase #6	$223.63	12.335%	$251.2148	$251.21	$251.20	$251.20
Purchase #7	$147.98	13.183%	$167.4882	$167.49	$167.50	$167.50
7 purchase totals =	$779.07		$851.6627	$851.66	$851.65	$851.60