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	$233.94	9.345%	$255.8017	$255.80	$255.80	$255.80
Purchase #2	$192.29	9.447%	$210.4556	$210.46	$210.45	$210.50
Purchase #3	$231.93	4.470%	$242.2973	$242.30	$242.30	$242.30
Purchase #4	$90.83	4.187%	$94.6331	$94.63	$94.65	$94.60
Purchase #5	$83.26	11.106%	$92.5069	$92.51	$92.50	$92.50
Purchase #6	$129.92	6.517%	$138.3869	$138.39	$138.40	$138.40
Purchase #7	$70.66	9.695%	$77.5105	$77.51	$77.50	$77.50
7 purchase totals =	$1,032.83		$1,111.5920	$1,111.60	$1,111.60	$1,111.60