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	$250.42	6.824%	$267.5087	$267.51	$267.50	$267.50
Purchase #2	$235.39	3.179%	$242.873	$242.87	$242.85	$242.90
Purchase #3	$85.70	11.425%	$95.4912	$95.49	$95.50	$95.50
Purchase #4	$79.70	7.190%	$85.4304	$85.43	$85.45	$85.40
Purchase #5	$67.91	9.697%	$74.4952	$74.50	$74.50	$74.50
Purchase #6	$56.87	5.164%	$59.8068	$59.81	$59.80	$59.80
Purchase #7	$222.35	13.551%	$252.4806	$252.48	$252.50	$252.50
7 purchase totals =	$998.34		$1,078.0859	$1,078.09	$1,078.10	$1,078.10