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	$17.52	10.110%	$19.2913	$19.29	$19.30	$19.30
Purchase #2	$122.29	4.563%	$127.8701	$127.87	$127.85	$127.90
Purchase #3	$99.70	10.197%	$109.8664	$109.87	$109.85	$109.90
Purchase #4	$140.45	3.118%	$144.8292	$144.83	$144.85	$144.80
Purchase #5	$193.75	11.781%	$216.5757	$216.58	$216.60	$216.60
Purchase #6	$59.45	8.503%	$64.505	$64.51	$64.50	$64.50
Purchase #7	$199.81	5.486%	$210.7716	$210.77	$210.75	$210.80
7 purchase totals =	$832.97		$893.7093	$893.72	$893.70	$893.80