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	$18.53	8.257%	$20.06	$20.06	$20.05	$20.10
Purchase #2	$92.88	11.202%	$103.2844	$103.28	$103.30	$103.30
Purchase #3	$148.91	4.451%	$155.538	$155.54	$155.55	$155.50
Purchase #4	$167.41	3.316%	$172.9613	$172.96	$172.95	$173.00
Purchase #5	$246.46	13.295%	$279.2269	$279.23	$279.25	$279.20
Purchase #6	$127.51	7.861%	$137.5336	$137.53	$137.55	$137.50
Purchase #7	$181.85	13.684%	$206.7344	$206.73	$206.75	$206.70
7 purchase totals =	$983.55		$1,075.3386	$1,075.33	$1,075.40	$1,075.30