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	$160.70	11.629%	$179.3878	$179.39	$179.40	$179.40
Purchase #2	$185.77	5.297%	$195.6102	$195.61	$195.60	$195.60
Purchase #3	$31.71	9.856%	$34.8353	$34.84	$34.85	$34.80
Purchase #4	$42.94	5.320%	$45.2244	$45.22	$45.20	$45.20
Purchase #5	$21.51	6.144%	$22.8316	$22.83	$22.85	$22.80
Purchase #6	$221.92	11.507%	$247.4563	$247.46	$247.45	$247.50
Purchase #7	$250.59	8.330%	$271.4641	$271.46	$271.45	$271.50
7 purchase totals =	$915.14		$996.8097	$996.81	$996.80	$996.80