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	$155.75	10.779%	$172.5383	$172.54	$172.55	$172.50
Purchase #2	$107.77	4.476%	$112.5938	$112.59	$112.60	$112.60
Purchase #3	$39.56	7.586%	$42.561	$42.56	$42.55	$42.60
Purchase #4	$173.29	13.407%	$196.523	$196.52	$196.50	$196.50
Purchase #5	$11.66	8.772%	$12.6828	$12.68	$12.70	$12.70
Purchase #6	$111.91	10.551%	$123.7176	$123.72	$123.70	$123.70
Purchase #7	$189.38	10.486%	$209.2384	$209.24	$209.25	$209.20
7 purchase totals =	$789.32		$869.8549	$869.85	$869.85	$869.80