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	$82.34	8.499%	$89.3381	$89.34	$89.35	$89.30
Purchase #2	$100.90	10.674%	$111.6701	$111.67	$111.65	$111.70
Purchase #3	$182.42	12.285%	$204.8303	$204.83	$204.85	$204.80
Purchase #4	$55.72	7.130%	$59.6928	$59.69	$59.70	$59.70
Purchase #5	$170.57	11.587%	$190.3339	$190.33	$190.35	$190.30
Purchase #6	$14.61	9.431%	$15.9879	$15.99	$16.00	$16.00
Purchase #7	$175.80	10.842%	$194.8602	$194.86	$194.85	$194.90
7 purchase totals =	$782.36		$866.7133	$866.71	$866.75	$866.70