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	$243.88	6.395%	$259.4761	$259.48	$259.50	$259.50
Purchase #2	$122.70	13.508%	$139.2743	$139.27	$139.25	$139.30
Purchase #3	$98.35	13.551%	$111.6774	$111.68	$111.70	$111.70
Purchase #4	$18.79	5.346%	$19.7945	$19.79	$19.80	$19.80
Purchase #5	$41.45	9.278%	$45.2957	$45.30	$45.30	$45.30
Purchase #6	$211.73	4.164%	$220.5464	$220.55	$220.55	$220.50
Purchase #7	$40.44	7.237%	$43.3666	$43.37	$43.35	$43.40
7 purchase totals =	$777.34		$839.4310	$839.44	$839.45	$839.50