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	$109.40	9.189%	$119.4528	$119.45	$119.45	$119.50
Purchase #2	$140.59	9.519%	$153.9728	$153.97	$153.95	$154.00
Purchase #3	$82.28	8.354%	$89.1537	$89.15	$89.15	$89.20
Purchase #4	$79.45	12.799%	$89.6188	$89.62	$89.60	$89.60
Purchase #5	$77.78	4.837%	$81.5422	$81.54	$81.55	$81.50
Purchase #6	$29.46	11.745%	$32.9201	$32.92	$32.90	$32.90
Purchase #7	$28.25	4.333%	$29.4741	$29.47	$29.45	$29.50
7 purchase totals =	$547.21		$596.1345	$596.12	$596.05	$596.20