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	$103.66	12.739%	$116.8652	$116.87	$116.85	$116.90
Purchase #2	$21.47	4.581%	$22.4535	$22.45	$22.45	$22.50
Purchase #3	$244.29	9.784%	$268.1913	$268.19	$268.20	$268.20
Purchase #4	$173.87	12.864%	$196.2366	$196.24	$196.25	$196.20
Purchase #5	$53.92	11.126%	$59.9191	$59.92	$59.90	$59.90
Purchase #6	$8.67	4.362%	$9.0482	$9.05	$9.05	$9.00
Purchase #7	$111.37	7.142%	$119.324	$119.32	$119.30	$119.30
7 purchase totals =	$717.25		$792.0379	$792.04	$792.00	$792.00