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	$66.61	4.671%	$69.7214	$69.72	$69.70	$69.70
Purchase #2	$60.90	8.500%	$66.0765	$66.08	$66.10	$66.10
Purchase #3	$101.42	3.867%	$105.3419	$105.34	$105.35	$105.30
Purchase #4	$232.32	12.240%	$260.756	$260.76	$260.75	$260.80
Purchase #5	$166.59	4.748%	$174.4997	$174.50	$174.50	$174.50
Purchase #6	$108.50	13.697%	$123.3612	$123.36	$123.35	$123.40
Purchase #7	$32.55	8.833%	$35.4251	$35.43	$35.45	$35.40
7 purchase totals =	$768.89		$835.1818	$835.19	$835.20	$835.20