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	$64.52	9.319%	$70.5326	$70.53	$70.55	$70.50
Purchase #2	$32.54	13.342%	$36.8815	$36.88	$36.90	$36.90
Purchase #3	$13.94	11.669%	$15.5667	$15.57	$15.55	$15.60
Purchase #4	$20.32	4.605%	$21.2557	$21.26	$21.25	$21.30
Purchase #5	$141.85	9.345%	$155.1059	$155.11	$155.10	$155.10
Purchase #6	$228.59	13.533%	$259.5251	$259.53	$259.55	$259.50
Purchase #7	$97.56	10.858%	$108.1531	$108.15	$108.15	$108.20
7 purchase totals =	$599.32		$667.0206	$667.03	$667.05	$667.10