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	$37.78	12.844%	$42.6325	$42.63	$42.65	$42.60
Purchase #2	$142.97	9.454%	$156.4864	$156.49	$156.50	$156.50
Purchase #3	$127.61	13.251%	$144.5196	$144.52	$144.50	$144.50
Purchase #4	$222.87	3.103%	$229.7857	$229.79	$229.80	$229.80
Purchase #5	$192.60	10.629%	$213.0715	$213.07	$213.05	$213.10
Purchase #6	$175.39	13.480%	$199.0326	$199.03	$199.05	$199.00
Purchase #7	$81.61	7.158%	$87.4516	$87.45	$87.45	$87.50
7 purchase totals =	$980.83		$1,072.9799	$1,072.98	$1,073.00	$1,073.00