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	$95.88	4.707%	$100.3931	$100.39	$100.40	$100.40
Purchase #2	$155.64	6.215%	$165.313	$165.31	$165.30	$165.30
Purchase #3	$31.32	12.538%	$35.2469	$35.25	$35.25	$35.20
Purchase #4	$27.99	10.447%	$30.9141	$30.91	$30.90	$30.90
Purchase #5	$74.90	10.516%	$82.7765	$82.78	$82.80	$82.80
Purchase #6	$230.31	12.654%	$259.4534	$259.45	$259.45	$259.50
Purchase #7	$35.49	10.245%	$39.126	$39.13	$39.15	$39.10
7 purchase totals =	$651.53		$713.2230	$713.22	$713.25	$713.20