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	$34.90	10.646%	$38.6155	$38.62	$38.60	$38.60
Purchase #2	$166.59	11.217%	$185.2764	$185.28	$185.30	$185.30
Purchase #3	$123.31	4.618%	$129.0045	$129.00	$129.00	$129.00
Purchase #4	$155.42	10.866%	$172.3079	$172.31	$172.30	$172.30
Purchase #5	$38.56	4.609%	$40.3372	$40.34	$40.35	$40.30
Purchase #6	$100.92	13.861%	$114.9085	$114.91	$114.90	$114.90
Purchase #7	$211.26	8.162%	$228.503	$228.50	$228.50	$228.50
7 purchase totals =	$830.96		$908.9530	$908.96	$908.95	$908.90