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	$223.46	6.773%	$238.5949	$238.59	$238.60	$238.60
Purchase #2	$67.37	6.485%	$71.7389	$71.74	$71.75	$71.70
Purchase #3	$150.33	5.683%	$158.8733	$158.87	$158.85	$158.90
Purchase #4	$16.76	12.567%	$18.8662	$18.87	$18.85	$18.90
Purchase #5	$194.79	8.777%	$211.8867	$211.89	$211.90	$211.90
Purchase #6	$117.53	8.181%	$127.1451	$127.15	$127.15	$127.10
Purchase #7	$159.46	5.236%	$167.8093	$167.81	$167.80	$167.80
7 purchase totals =	$929.70		$994.9144	$994.92	$994.90	$994.90