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	$208.67	12.758%	$235.2921	$235.29	$235.30	$235.30
Purchase #2	$155.87	3.469%	$161.2771	$161.28	$161.30	$161.30
Purchase #3	$132.60	7.848%	$143.0064	$143.01	$143.00	$143.00
Purchase #4	$180.77	4.458%	$188.8287	$188.83	$188.85	$188.80
Purchase #5	$29.45	13.173%	$33.3294	$33.33	$33.35	$33.30
Purchase #6	$96.89	13.212%	$109.6911	$109.69	$109.70	$109.70
Purchase #7	$138.26	6.116%	$146.716	$146.72	$146.70	$146.70
7 purchase totals =	$942.51		$1,018.1408	$1,018.15	$1,018.20	$1,018.10