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	$116.87	12.232%	$131.1655	$131.17	$131.15	$131.20
Purchase #2	$95.80	13.178%	$108.4245	$108.42	$108.40	$108.40
Purchase #3	$175.74	5.768%	$185.8767	$185.88	$185.90	$185.90
Purchase #4	$148.86	13.191%	$168.4961	$168.50	$168.50	$168.50
Purchase #5	$176.55	4.630%	$184.7243	$184.72	$184.70	$184.70
Purchase #6	$78.62	8.330%	$85.169	$85.17	$85.15	$85.20
Purchase #7	$91.29	4.847%	$95.7148	$95.71	$95.70	$95.70
7 purchase totals =	$883.73		$959.5709	$959.57	$959.50	$959.60