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	$11.81	12.742%	$13.3148	$13.31	$13.30	$13.30
Purchase #2	$145.29	6.579%	$154.8486	$154.85	$154.85	$154.80
Purchase #3	$95.50	7.281%	$102.4534	$102.45	$102.45	$102.50
Purchase #4	$144.96	4.352%	$151.2687	$151.27	$151.25	$151.30
Purchase #5	$72.69	8.505%	$78.8723	$78.87	$78.85	$78.90
Purchase #6	$144.71	5.317%	$152.4042	$152.40	$152.40	$152.40
Purchase #7	$8.62	9.709%	$9.4569	$9.46	$9.45	$9.50
7 purchase totals =	$623.58		$662.6189	$662.61	$662.55	$662.70