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	$158.55	12.848%	$178.9205	$178.92	$178.90	$178.90
Purchase #2	$194.57	12.171%	$218.2511	$218.25	$218.25	$218.30
Purchase #3	$124.93	7.359%	$134.1236	$134.12	$134.10	$134.10
Purchase #4	$28.52	12.629%	$32.1218	$32.12	$32.10	$32.10
Purchase #5	$231.66	9.857%	$254.4947	$254.49	$254.50	$254.50
Purchase #6	$127.39	11.465%	$141.9953	$142.00	$142.00	$142.00
Purchase #7	$185.70	12.158%	$208.2774	$208.28	$208.30	$208.30
7 purchase totals =	$1,051.32		$1,168.1844	$1,168.18	$1,168.15	$1,168.20