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	$67.61	10.685%	$74.8341	$74.83	$74.85	$74.80
Purchase #2	$154.73	12.493%	$174.0604	$174.06	$174.05	$174.10
Purchase #3	$164.55	11.296%	$183.1376	$183.14	$183.15	$183.10
Purchase #4	$233.45	3.864%	$242.4705	$242.47	$242.45	$242.50
Purchase #5	$71.91	8.651%	$78.1309	$78.13	$78.15	$78.10
Purchase #6	$203.48	3.412%	$210.4227	$210.42	$210.40	$210.40
Purchase #7	$44.31	13.454%	$50.2715	$50.27	$50.25	$50.30
7 purchase totals =	$940.04		$1,013.3277	$1,013.32	$1,013.30	$1,013.30