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	$170.53	6.806%	$182.1363	$182.14	$182.15	$182.10
Purchase #2	$49.79	6.212%	$52.883	$52.88	$52.90	$52.90
Purchase #3	$95.61	5.362%	$100.7366	$100.74	$100.75	$100.70
Purchase #4	$20.84	7.194%	$22.3392	$22.34	$22.35	$22.30
Purchase #5	$183.99	3.343%	$190.1408	$190.14	$190.15	$190.10
Purchase #6	$100.54	5.177%	$105.745	$105.75	$105.75	$105.70
Purchase #7	$53.45	6.352%	$56.8451	$56.85	$56.85	$56.80
7 purchase totals =	$674.75		$710.8260	$710.84	$710.90	$710.60