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	$45.81	9.438%	$50.1335	$50.13	$50.15	$50.10
Purchase #2	$190.37	12.538%	$214.2386	$214.24	$214.25	$214.20
Purchase #3	$180.46	8.211%	$195.2776	$195.28	$195.30	$195.30
Purchase #4	$185.42	6.206%	$196.9272	$196.93	$196.95	$196.90
Purchase #5	$10.69	12.167%	$11.9907	$11.99	$12.00	$12.00
Purchase #6	$145.82	11.537%	$162.6433	$162.64	$162.65	$162.60
Purchase #7	$96.80	3.813%	$100.491	$100.49	$100.50	$100.50
7 purchase totals =	$855.37		$931.7019	$931.70	$931.80	$931.60