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	$103.71	6.342%	$110.2873	$110.29	$110.30	$110.30
Purchase #2	$33.89	13.527%	$38.4743	$38.47	$38.45	$38.50
Purchase #3	$48.51	3.186%	$50.0555	$50.06	$50.05	$50.10
Purchase #4	$18.33	4.585%	$19.1704	$19.17	$19.15	$19.20
Purchase #5	$131.45	7.116%	$140.804	$140.80	$140.80	$140.80
Purchase #6	$150.38	5.698%	$158.9487	$158.95	$158.95	$158.90
Purchase #7	$31.53	9.288%	$34.4585	$34.46	$34.45	$34.50
7 purchase totals =	$517.80		$552.1987	$552.20	$552.15	$552.30