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	$44.39	13.252%	$50.2726	$50.27	$50.25	$50.30
Purchase #2	$168.25	6.649%	$179.4369	$179.44	$179.45	$179.40
Purchase #3	$166.27	3.806%	$172.5982	$172.60	$172.60	$172.60
Purchase #4	$50.45	12.362%	$56.6866	$56.69	$56.70	$56.70
Purchase #5	$41.52	4.586%	$43.4241	$43.42	$43.40	$43.40
Purchase #6	$217.87	13.546%	$247.3827	$247.38	$247.40	$247.40
Purchase #7	$153.30	10.745%	$169.7721	$169.77	$169.75	$169.80
7 purchase totals =	$842.05		$919.5732	$919.57	$919.55	$919.60