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	$170.77	8.575%	$185.4135	$185.41	$185.40	$185.40
Purchase #2	$144.58	10.239%	$159.3835	$159.38	$159.40	$159.40
Purchase #3	$90.82	10.682%	$100.5214	$100.52	$100.50	$100.50
Purchase #4	$166.84	5.344%	$175.7559	$175.76	$175.75	$175.80
Purchase #5	$131.29	5.669%	$138.7328	$138.73	$138.75	$138.70
Purchase #6	$66.65	9.701%	$73.1157	$73.12	$73.10	$73.10
Purchase #7	$160.89	4.164%	$167.5895	$167.59	$167.60	$167.60
7 purchase totals =	$931.84		$1,000.5123	$1,000.51	$1,000.50	$1,000.50