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	$205.54	12.250%	$230.7187	$230.72	$230.70	$230.70
Purchase #2	$155.84	11.344%	$173.5185	$173.52	$173.50	$173.50
Purchase #3	$100.75	3.637%	$104.4143	$104.41	$104.40	$104.40
Purchase #4	$150.74	3.170%	$155.5185	$155.52	$155.50	$155.50
Purchase #5	$221.46	7.710%	$238.5346	$238.53	$238.55	$238.50
Purchase #6	$78.25	4.634%	$81.8761	$81.88	$81.90	$81.90
Purchase #7	$134.82	8.474%	$146.2446	$146.24	$146.25	$146.20
7 purchase totals =	$1,047.40		$1,130.8253	$1,130.82	$1,130.80	$1,130.70