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	$132.72	11.756%	$148.3226	$148.32	$148.30	$148.30
Purchase #2	$171.33	8.203%	$185.3842	$185.38	$185.40	$185.40
Purchase #3	$129.94	9.672%	$142.5078	$142.51	$142.50	$142.50
Purchase #4	$139.54	3.517%	$144.4476	$144.45	$144.45	$144.40
Purchase #5	$69.60	6.524%	$74.1407	$74.14	$74.15	$74.10
Purchase #6	$25.41	12.135%	$28.4935	$28.49	$28.50	$28.50
Purchase #7	$14.90	4.285%	$15.5385	$15.54	$15.55	$15.50
7 purchase totals =	$683.44		$738.8349	$738.83	$738.85	$738.70