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	$213.25	12.206%	$239.2793	$239.28	$239.30	$239.30
Purchase #2	$129.30	7.673%	$139.2212	$139.22	$139.20	$139.20
Purchase #3	$158.57	12.353%	$178.1582	$178.16	$178.15	$178.20
Purchase #4	$80.49	7.779%	$86.7513	$86.75	$86.75	$86.80
Purchase #5	$100.98	10.723%	$111.8081	$111.81	$111.80	$111.80
Purchase #6	$245.33	7.754%	$264.3529	$264.35	$264.35	$264.40
Purchase #7	$237.66	7.588%	$255.6936	$255.69	$255.70	$255.70
7 purchase totals =	$1,165.58		$1,275.2646	$1,275.26	$1,275.25	$1,275.40