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	$80.68	12.137%	$90.4721	$90.47	$90.45	$90.50
Purchase #2	$215.57	4.663%	$225.622	$225.62	$225.60	$225.60
Purchase #3	$166.61	3.371%	$172.2264	$172.23	$172.25	$172.20
Purchase #4	$15.44	11.747%	$17.2537	$17.25	$17.25	$17.30
Purchase #5	$72.69	5.389%	$76.6073	$76.61	$76.60	$76.60
Purchase #6	$171.54	5.703%	$181.3229	$181.32	$181.30	$181.30
Purchase #7	$49.99	6.570%	$53.2743	$53.27	$53.25	$53.30
7 purchase totals =	$772.52		$816.7787	$816.77	$816.70	$816.80