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	$101.29	9.858%	$111.2752	$111.28	$111.30	$111.30
Purchase #2	$205.36	8.188%	$222.1749	$222.17	$222.15	$222.20
Purchase #3	$197.86	7.360%	$212.4225	$212.42	$212.40	$212.40
Purchase #4	$14.44	10.318%	$15.9299	$15.93	$15.95	$15.90
Purchase #5	$112.52	10.755%	$124.6215	$124.62	$124.60	$124.60
Purchase #6	$50.85	10.600%	$56.2401	$56.24	$56.25	$56.20
Purchase #7	$109.70	3.465%	$113.5011	$113.50	$113.50	$113.50
7 purchase totals =	$792.02		$856.1652	$856.16	$856.15	$856.10