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	$27.73	12.331%	$31.1494	$31.15	$31.15	$31.10
Purchase #2	$78.88	5.668%	$83.3509	$83.35	$83.35	$83.40
Purchase #3	$75.82	7.699%	$81.6574	$81.66	$81.65	$81.70
Purchase #4	$151.72	5.143%	$159.523	$159.52	$159.50	$159.50
Purchase #5	$68.35	6.313%	$72.6649	$72.66	$72.65	$72.70
Purchase #6	$29.79	12.424%	$33.4911	$33.49	$33.50	$33.50
Purchase #7	$207.69	12.579%	$233.8153	$233.82	$233.80	$233.80
7 purchase totals =	$639.98		$695.6520	$695.65	$695.60	$695.70