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	$66.26	9.740%	$72.7137	$72.71	$72.70	$72.70
Purchase #2	$125.96	13.419%	$142.8626	$142.86	$142.85	$142.90
Purchase #3	$214.57	13.510%	$243.5584	$243.56	$243.55	$243.60
Purchase #4	$33.67	13.581%	$38.2427	$38.24	$38.25	$38.20
Purchase #5	$46.35	12.121%	$51.9681	$51.97	$51.95	$52.00
Purchase #6	$184.67	3.742%	$191.5804	$191.58	$191.60	$191.60
Purchase #7	$108.67	3.594%	$112.5756	$112.58	$112.60	$112.60
7 purchase totals =	$780.15		$853.5015	$853.50	$853.50	$853.60