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	$132.37	10.559%	$146.3469	$146.35	$146.35	$146.30
Purchase #2	$209.76	12.585%	$236.1583	$236.16	$236.15	$236.20
Purchase #3	$77.70	8.329%	$84.1716	$84.17	$84.15	$84.20
Purchase #4	$100.63	10.849%	$111.5473	$111.55	$111.55	$111.50
Purchase #5	$105.91	5.556%	$111.7944	$111.79	$111.80	$111.80
Purchase #6	$17.61	11.360%	$19.6105	$19.61	$19.60	$19.60
Purchase #7	$246.70	5.231%	$259.6049	$259.60	$259.60	$259.60
7 purchase totals =	$890.68		$969.2339	$969.23	$969.20	$969.20