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	$50.86	6.781%	$54.3088	$54.31	$54.30	$54.30
Purchase #2	$46.98	11.571%	$52.4161	$52.42	$52.40	$52.40
Purchase #3	$135.73	7.447%	$145.8378	$145.84	$145.85	$145.80
Purchase #4	$146.45	10.198%	$161.385	$161.39	$161.40	$161.40
Purchase #5	$207.25	5.768%	$219.2042	$219.20	$219.20	$219.20
Purchase #6	$77.93	13.230%	$88.2401	$88.24	$88.25	$88.20
Purchase #7	$55.28	7.640%	$59.5034	$59.50	$59.50	$59.50
7 purchase totals =	$720.48		$780.8954	$780.90	$780.90	$780.80