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	$80.57	6.702%	$85.9698	$85.97	$85.95	$86.00
Purchase #2	$79.42	4.322%	$82.8525	$82.85	$82.85	$82.90
Purchase #3	$236.47	11.331%	$263.2644	$263.26	$263.25	$263.30
Purchase #4	$171.32	12.588%	$192.8858	$192.89	$192.90	$192.90
Purchase #5	$73.75	13.353%	$83.5978	$83.60	$83.60	$83.60
Purchase #6	$129.65	7.610%	$139.5164	$139.52	$139.50	$139.50
Purchase #7	$126.28	8.510%	$137.0264	$137.03	$137.05	$137.00
7 purchase totals =	$897.46		$985.1131	$985.12	$985.10	$985.20