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	$42.41	8.243%	$45.9059	$45.91	$45.90	$45.90
Purchase #2	$234.63	6.806%	$250.5989	$250.60	$250.60	$250.60
Purchase #3	$160.64	4.329%	$167.5941	$167.59	$167.60	$167.60
Purchase #4	$210.56	5.735%	$222.6356	$222.64	$222.65	$222.60
Purchase #5	$250.30	3.162%	$258.2145	$258.21	$258.20	$258.20
Purchase #6	$140.64	4.278%	$146.6566	$146.66	$146.65	$146.70
Purchase #7	$163.64	6.797%	$174.7626	$174.76	$174.75	$174.80
7 purchase totals =	$1,202.82		$1,266.3682	$1,266.37	$1,266.35	$1,266.40