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	$178.93	3.761%	$185.6596	$185.66	$185.65	$185.70
Purchase #2	$205.36	9.725%	$225.3313	$225.33	$225.35	$225.30
Purchase #3	$99.86	4.764%	$104.6173	$104.62	$104.60	$104.60
Purchase #4	$137.95	10.550%	$152.5037	$152.50	$152.50	$152.50
Purchase #5	$151.46	11.583%	$169.0036	$169.00	$169.00	$169.00
Purchase #6	$158.79	8.835%	$172.8191	$172.82	$172.80	$172.80
Purchase #7	$123.42	6.770%	$131.7755	$131.78	$131.80	$131.80
7 purchase totals =	$1,055.77		$1,141.7101	$1,141.71	$1,141.70	$1,141.70