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	$13.70	10.773%	$15.1759	$15.18	$15.20	$15.20
Purchase #2	$244.75	12.608%	$275.6081	$275.61	$275.60	$275.60
Purchase #3	$110.36	9.109%	$120.4127	$120.41	$120.40	$120.40
Purchase #4	$130.43	9.260%	$142.5078	$142.51	$142.50	$142.50
Purchase #5	$241.73	4.711%	$253.1179	$253.12	$253.10	$253.10
Purchase #6	$70.56	9.464%	$77.2378	$77.24	$77.25	$77.20
Purchase #7	$174.68	7.308%	$187.4456	$187.45	$187.45	$187.40
7 purchase totals =	$986.21		$1,071.5058	$1,071.52	$1,071.50	$1,071.40