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	$243.82	8.306%	$264.0717	$264.07	$264.05	$264.10
Purchase #2	$208.77	9.144%	$227.8599	$227.86	$227.85	$227.90
Purchase #3	$17.28	5.667%	$18.2593	$18.26	$18.25	$18.30
Purchase #4	$103.37	10.753%	$114.4854	$114.49	$114.50	$114.50
Purchase #5	$126.47	7.677%	$136.1791	$136.18	$136.20	$136.20
Purchase #6	$126.25	11.242%	$140.443	$140.44	$140.45	$140.40
Purchase #7	$98.42	13.763%	$111.9655	$111.97	$111.95	$112.00
7 purchase totals =	$924.38		$1,013.2639	$1,013.27	$1,013.25	$1,013.40