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	$128.80	7.561%	$138.5386	$138.54	$138.55	$138.50
Purchase #2	$49.93	11.436%	$55.64	$55.64	$55.65	$55.60
Purchase #3	$162.83	3.581%	$168.6609	$168.66	$168.65	$168.70
Purchase #4	$108.67	10.699%	$120.2966	$120.30	$120.30	$120.30
Purchase #5	$96.75	4.228%	$100.8406	$100.84	$100.85	$100.80
Purchase #6	$171.51	8.399%	$185.9151	$185.92	$185.90	$185.90
Purchase #7	$9.48	13.628%	$10.7719	$10.77	$10.75	$10.80
7 purchase totals =	$727.97		$780.6637	$780.67	$780.65	$780.60