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	$245.69	7.723%	$264.6646	$264.66	$264.65	$264.70
Purchase #2	$198.85	12.257%	$223.223	$223.22	$223.20	$223.20
Purchase #3	$145.32	11.606%	$162.1858	$162.19	$162.20	$162.20
Purchase #4	$164.58	3.287%	$169.9897	$169.99	$170.00	$170.00
Purchase #5	$118.74	7.377%	$127.4994	$127.50	$127.50	$127.50
Purchase #6	$160.45	4.595%	$167.8227	$167.82	$167.80	$167.80
Purchase #7	$134.31	6.845%	$143.5035	$143.50	$143.50	$143.50
7 purchase totals =	$1,167.94		$1,258.8887	$1,258.88	$1,258.85	$1,258.90