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	$231.93	5.249%	$244.104	$244.10	$244.10	$244.10
Purchase #2	$137.86	11.709%	$154.002	$154.00	$154.00	$154.00
Purchase #3	$199.58	11.330%	$222.1924	$222.19	$222.20	$222.20
Purchase #4	$62.35	6.838%	$66.6135	$66.61	$66.60	$66.60
Purchase #5	$153.81	8.158%	$166.3578	$166.36	$166.35	$166.40
Purchase #6	$27.90	9.669%	$30.5977	$30.60	$30.60	$30.60
Purchase #7	$37.82	11.758%	$42.2669	$42.27	$42.25	$42.30
7 purchase totals =	$851.25		$926.1343	$926.13	$926.10	$926.20