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	$18.78	7.869%	$20.2578	$20.26	$20.25	$20.30
Purchase #2	$234.95	12.596%	$264.5443	$264.54	$264.55	$264.50
Purchase #3	$7.82	10.801%	$8.6646	$8.66	$8.65	$8.70
Purchase #4	$218.79	13.340%	$247.9766	$247.98	$248.00	$248.00
Purchase #5	$137.74	7.680%	$148.3184	$148.32	$148.30	$148.30
Purchase #6	$38.92	9.505%	$42.6193	$42.62	$42.60	$42.60
Purchase #7	$176.89	4.547%	$184.9332	$184.93	$184.95	$184.90
7 purchase totals =	$833.89		$917.3142	$917.31	$917.30	$917.30