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	$222.42	12.641%	$250.5361	$250.54	$250.55	$250.50
Purchase #2	$146.91	8.666%	$159.6412	$159.64	$159.65	$159.60
Purchase #3	$134.97	5.622%	$142.558	$142.56	$142.55	$142.60
Purchase #4	$202.66	9.829%	$222.5795	$222.58	$222.60	$222.60
Purchase #5	$164.55	11.509%	$183.4881	$183.49	$183.50	$183.50
Purchase #6	$115.98	7.543%	$124.7284	$124.73	$124.75	$124.70
Purchase #7	$42.80	6.191%	$45.4497	$45.45	$45.45	$45.40
7 purchase totals =	$1,030.29		$1,128.9810	$1,128.99	$1,129.05	$1,128.90