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	$226.41	5.201%	$238.1856	$238.19	$238.20	$238.20
Purchase #2	$158.83	13.205%	$179.8035	$179.80	$179.80	$179.80
Purchase #3	$30.77	9.169%	$33.5913	$33.59	$33.60	$33.60
Purchase #4	$109.87	6.726%	$117.2599	$117.26	$117.25	$117.30
Purchase #5	$185.95	6.691%	$198.3919	$198.39	$198.40	$198.40
Purchase #6	$122.52	4.384%	$127.8913	$127.89	$127.90	$127.90
Purchase #7	$82.54	4.776%	$86.4821	$86.48	$86.50	$86.50
7 purchase totals =	$916.89		$981.6056	$981.60	$981.65	$981.70