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	$59.82	12.388%	$67.2305	$67.23	$67.25	$67.20
Purchase #2	$149.78	6.204%	$159.0724	$159.07	$159.05	$159.10
Purchase #3	$119.27	8.867%	$129.8457	$129.85	$129.85	$129.80
Purchase #4	$93.59	7.212%	$100.3397	$100.34	$100.35	$100.30
Purchase #5	$70.80	10.808%	$78.4521	$78.45	$78.45	$78.50
Purchase #6	$145.83	11.609%	$162.7594	$162.76	$162.75	$162.80
Purchase #7	$110.75	4.839%	$116.1092	$116.11	$116.10	$116.10
7 purchase totals =	$749.84		$813.8090	$813.81	$813.80	$813.80