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	$160.84	7.257%	$172.5122	$172.51	$172.50	$172.50
Purchase #2	$24.66	11.520%	$27.5008	$27.50	$27.50	$27.50
Purchase #3	$124.95	3.180%	$128.9234	$128.92	$128.90	$128.90
Purchase #4	$205.50	8.686%	$223.3497	$223.35	$223.35	$223.30
Purchase #5	$222.62	11.205%	$247.5646	$247.56	$247.55	$247.60
Purchase #6	$154.29	11.119%	$171.4455	$171.45	$171.45	$171.40
Purchase #7	$140.50	8.296%	$152.1559	$152.16	$152.15	$152.20
7 purchase totals =	$1,033.36		$1,123.4521	$1,123.45	$1,123.40	$1,123.40