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	$81.62	7.472%	$87.7186	$87.72	$87.70	$87.70
Purchase #2	$56.41	6.228%	$59.9232	$59.92	$59.90	$59.90
Purchase #3	$168.54	10.601%	$186.4069	$186.41	$186.40	$186.40
Purchase #4	$215.78	8.718%	$234.5917	$234.59	$234.60	$234.60
Purchase #5	$155.30	12.671%	$174.9781	$174.98	$175.00	$175.00
Purchase #6	$77.82	7.819%	$83.9047	$83.90	$83.90	$83.90
Purchase #7	$130.26	9.404%	$142.5097	$142.51	$142.50	$142.50
7 purchase totals =	$885.73		$970.0329	$970.03	$970.00	$970.00