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	$94.59	13.671%	$107.5214	$107.52	$107.50	$107.50
Purchase #2	$53.56	9.845%	$58.833	$58.83	$58.85	$58.80
Purchase #3	$79.64	7.464%	$85.5843	$85.58	$85.60	$85.60
Purchase #4	$237.46	8.772%	$258.29	$258.29	$258.30	$258.30
Purchase #5	$37.72	4.496%	$39.4159	$39.42	$39.40	$39.40
Purchase #6	$35.41	8.735%	$38.5031	$38.50	$38.50	$38.50
Purchase #7	$215.76	12.586%	$242.9156	$242.92	$242.90	$242.90
7 purchase totals =	$754.14		$831.0633	$831.06	$831.05	$831.00