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	$77.33	10.376%	$85.3538	$85.35	$85.35	$85.40
Purchase #2	$18.76	10.233%	$20.6797	$20.68	$20.70	$20.70
Purchase #3	$19.31	7.214%	$20.703	$20.70	$20.70	$20.70
Purchase #4	$238.95	11.478%	$266.3767	$266.38	$266.40	$266.40
Purchase #5	$52.74	12.420%	$59.2903	$59.29	$59.30	$59.30
Purchase #6	$73.48	12.717%	$82.8245	$82.82	$82.80	$82.80
Purchase #7	$100.56	5.123%	$105.7117	$105.71	$105.70	$105.70
7 purchase totals =	$581.13		$640.9397	$640.93	$640.95	$641.00