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	$250.99	9.624%	$275.1453	$275.15	$275.15	$275.10
Purchase #2	$17.85	13.459%	$20.2524	$20.25	$20.25	$20.30
Purchase #3	$41.66	4.686%	$43.6122	$43.61	$43.60	$43.60
Purchase #4	$200.76	10.188%	$221.2134	$221.21	$221.20	$221.20
Purchase #5	$5.49	3.555%	$5.6852	$5.69	$5.70	$5.70
Purchase #6	$112.91	5.271%	$118.8615	$118.86	$118.85	$118.90
Purchase #7	$136.30	10.845%	$151.0817	$151.08	$151.10	$151.10
7 purchase totals =	$765.96		$835.8517	$835.85	$835.85	$835.90