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	$103.43	10.611%	$114.405	$114.41	$114.40	$114.40
Purchase #2	$143.69	8.201%	$155.474	$155.47	$155.45	$155.50
Purchase #3	$73.96	5.810%	$78.2571	$78.26	$78.25	$78.30
Purchase #4	$84.26	12.102%	$94.4571	$94.46	$94.45	$94.50
Purchase #5	$106.98	4.848%	$112.1664	$112.17	$112.15	$112.20
Purchase #6	$19.79	3.692%	$20.5206	$20.52	$20.50	$20.50
Purchase #7	$219.45	13.852%	$249.8482	$249.85	$249.85	$249.80
7 purchase totals =	$751.56		$825.1284	$825.14	$825.05	$825.20