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	$227.62	13.682%	$258.763	$258.76	$258.75	$258.80
Purchase #2	$155.32	9.552%	$170.1562	$170.16	$170.15	$170.20
Purchase #3	$206.77	7.604%	$222.4928	$222.49	$222.50	$222.50
Purchase #4	$172.66	4.159%	$179.8409	$179.84	$179.85	$179.80
Purchase #5	$6.50	11.808%	$7.2675	$7.27	$7.25	$7.30
Purchase #6	$57.33	11.772%	$64.0789	$64.08	$64.10	$64.10
Purchase #7	$119.70	6.472%	$127.447	$127.45	$127.45	$127.40
7 purchase totals =	$945.90		$1,030.0463	$1,030.05	$1,030.05	$1,030.10