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	$17.57	4.380%	$18.3396	$18.34	$18.35	$18.30
Purchase #2	$89.45	13.669%	$101.6769	$101.68	$101.70	$101.70
Purchase #3	$229.60	11.153%	$255.2073	$255.21	$255.20	$255.20
Purchase #4	$139.28	9.345%	$152.2957	$152.30	$152.30	$152.30
Purchase #5	$38.30	13.633%	$43.5214	$43.52	$43.50	$43.50
Purchase #6	$122.68	9.159%	$133.9163	$133.92	$133.90	$133.90
Purchase #7	$238.80	10.654%	$264.2418	$264.24	$264.25	$264.20
7 purchase totals =	$875.68		$969.1990	$969.21	$969.20	$969.10