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	$234.57	12.769%	$264.5222	$264.52	$264.50	$264.50
Purchase #2	$33.34	3.262%	$34.4276	$34.43	$34.45	$34.40
Purchase #3	$145.31	10.638%	$160.7681	$160.77	$160.75	$160.80
Purchase #4	$60.39	4.836%	$63.3105	$63.31	$63.30	$63.30
Purchase #5	$149.64	10.561%	$165.4435	$165.44	$165.45	$165.40
Purchase #6	$185.80	4.635%	$194.4118	$194.41	$194.40	$194.40
Purchase #7	$174.76	5.194%	$183.837	$183.84	$183.85	$183.80
7 purchase totals =	$983.81		$1,066.7207	$1,066.72	$1,066.70	$1,066.60