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	$33.51	5.758%	$35.4395	$35.44	$35.45	$35.40
Purchase #2	$29.53	8.255%	$31.9677	$31.97	$31.95	$32.00
Purchase #3	$122.71	13.796%	$139.6391	$139.64	$139.65	$139.60
Purchase #4	$37.56	7.356%	$40.3229	$40.32	$40.30	$40.30
Purchase #5	$66.32	11.420%	$73.8937	$73.89	$73.90	$73.90
Purchase #6	$222.58	4.805%	$233.275	$233.28	$233.30	$233.30
Purchase #7	$101.95	10.560%	$112.7159	$112.72	$112.70	$112.70
7 purchase totals =	$614.16		$667.2538	$667.26	$667.25	$667.20