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	$11.56	5.337%	$12.177	$12.18	$12.20	$12.20
Purchase #2	$61.76	11.137%	$68.6382	$68.64	$68.65	$68.60
Purchase #3	$42.31	3.732%	$43.889	$43.89	$43.90	$43.90
Purchase #4	$17.85	5.116%	$18.7632	$18.76	$18.75	$18.80
Purchase #5	$95.61	5.527%	$100.8944	$100.89	$100.90	$100.90
Purchase #6	$104.69	11.467%	$116.6948	$116.69	$116.70	$116.70
Purchase #7	$26.71	6.537%	$28.456	$28.46	$28.45	$28.50
7 purchase totals =	$360.49		$389.5126	$389.51	$389.55	$389.60