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	$13.99	13.868%	$15.9301	$15.93	$15.95	$15.90
Purchase #2	$55.81	8.358%	$60.4746	$60.47	$60.45	$60.50
Purchase #3	$105.71	5.471%	$111.4934	$111.49	$111.50	$111.50
Purchase #4	$96.46	3.529%	$99.8641	$99.86	$99.85	$99.90
Purchase #5	$30.53	10.482%	$33.7302	$33.73	$33.75	$33.70
Purchase #6	$150.62	10.505%	$166.4426	$166.44	$166.45	$166.40
Purchase #7	$184.30	12.448%	$207.2417	$207.24	$207.25	$207.20
7 purchase totals =	$637.42		$695.1767	$695.16	$695.20	$695.10