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	$134.89	3.729%	$139.92	$139.92	$139.90	$139.90
Purchase #2	$24.71	11.117%	$27.457	$27.46	$27.45	$27.50
Purchase #3	$31.65	13.663%	$35.9743	$35.97	$35.95	$36.00
Purchase #4	$111.99	13.806%	$127.4513	$127.45	$127.45	$127.50
Purchase #5	$52.26	8.283%	$56.5887	$56.59	$56.60	$56.60
Purchase #6	$147.53	7.535%	$158.6464	$158.65	$158.65	$158.60
Purchase #7	$94.92	5.216%	$99.871	$99.87	$99.85	$99.90
7 purchase totals =	$597.95		$645.9087	$645.91	$645.85	$646.00