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	$92.70	4.447%	$96.8224	$96.82	$96.80	$96.80
Purchase #2	$199.69	11.205%	$222.0653	$222.07	$222.05	$222.10
Purchase #3	$112.43	9.432%	$123.0344	$123.03	$123.05	$123.00
Purchase #4	$56.77	5.367%	$59.8168	$59.82	$59.80	$59.80
Purchase #5	$210.26	9.117%	$229.4294	$229.43	$229.45	$229.40
Purchase #6	$154.50	3.656%	$160.1485	$160.15	$160.15	$160.10
Purchase #7	$18.53	7.829%	$19.9807	$19.98	$20.00	$20.00
7 purchase totals =	$844.88		$911.2975	$911.30	$911.30	$911.20