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	$12.76	5.510%	$13.4631	$13.46	$13.45	$13.50
Purchase #2	$65.48	5.252%	$68.919	$68.92	$68.90	$68.90
Purchase #3	$72.88	6.348%	$77.5064	$77.51	$77.50	$77.50
Purchase #4	$79.64	4.799%	$83.4619	$83.46	$83.45	$83.50
Purchase #5	$31.89	7.144%	$34.1682	$34.17	$34.15	$34.20
Purchase #6	$145.57	3.639%	$150.8673	$150.87	$150.85	$150.90
Purchase #7	$235.74	4.408%	$246.1314	$246.13	$246.15	$246.10
7 purchase totals =	$643.96		$674.5173	$674.52	$674.45	$674.60