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	$21.49	4.186%	$22.3896	$22.39	$22.40	$22.40
Purchase #2	$68.58	11.676%	$76.5874	$76.59	$76.60	$76.60
Purchase #3	$95.67	13.391%	$108.4812	$108.48	$108.50	$108.50
Purchase #4	$96.82	6.709%	$103.3157	$103.32	$103.30	$103.30
Purchase #5	$70.39	12.612%	$79.2676	$79.27	$79.25	$79.30
Purchase #6	$80.51	11.271%	$89.5843	$89.58	$89.60	$89.60
Purchase #7	$127.34	8.803%	$138.5497	$138.55	$138.55	$138.50
7 purchase totals =	$560.80		$618.1755	$618.18	$618.20	$618.20