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	$22.80	8.539%	$24.7469	$24.75	$24.75	$24.70
Purchase #2	$238.44	7.750%	$256.9191	$256.92	$256.90	$256.90
Purchase #3	$99.57	9.799%	$109.3269	$109.33	$109.35	$109.30
Purchase #4	$102.58	13.305%	$116.2283	$116.23	$116.25	$116.20
Purchase #5	$65.29	6.477%	$69.5188	$69.52	$69.50	$69.50
Purchase #6	$208.36	4.540%	$217.8195	$217.82	$217.80	$217.80
Purchase #7	$55.90	10.180%	$61.5906	$61.59	$61.60	$61.60
7 purchase totals =	$792.94		$856.1501	$856.16	$856.15	$856.00