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	$154.49	4.330%	$161.1794	$161.18	$161.20	$161.20
Purchase #2	$243.45	8.651%	$264.5109	$264.51	$264.50	$264.50
Purchase #3	$200.56	4.673%	$209.9322	$209.93	$209.95	$209.90
Purchase #4	$82.91	9.182%	$90.5228	$90.52	$90.50	$90.50
Purchase #5	$157.31	6.477%	$167.499	$167.50	$167.50	$167.50
Purchase #6	$127.42	4.389%	$133.0125	$133.01	$133.00	$133.00
Purchase #7	$172.63	13.301%	$195.5915	$195.59	$195.60	$195.60
7 purchase totals =	$1,138.77		$1,222.2483	$1,222.24	$1,222.25	$1,222.20