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	$112.98	6.677%	$120.5237	$120.52	$120.50	$120.50
Purchase #2	$114.46	7.399%	$122.9289	$122.93	$122.95	$122.90
Purchase #3	$108.90	13.502%	$123.6037	$123.60	$123.60	$123.60
Purchase #4	$205.90	13.587%	$233.8756	$233.88	$233.90	$233.90
Purchase #5	$79.55	5.177%	$83.6683	$83.67	$83.65	$83.70
Purchase #6	$62.61	4.507%	$65.4318	$65.43	$65.45	$65.40
Purchase #7	$151.27	4.548%	$158.1498	$158.15	$158.15	$158.10
7 purchase totals =	$835.67		$908.1818	$908.18	$908.20	$908.10