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	$133.27	6.411%	$141.8139	$141.81	$141.80	$141.80
Purchase #2	$172.70	10.812%	$191.3723	$191.37	$191.35	$191.40
Purchase #3	$80.92	8.240%	$87.5878	$87.59	$87.60	$87.60
Purchase #4	$209.69	9.234%	$229.0528	$229.05	$229.05	$229.10
Purchase #5	$240.27	6.789%	$256.5819	$256.58	$256.60	$256.60
Purchase #6	$92.49	13.863%	$105.3119	$105.31	$105.30	$105.30
Purchase #7	$187.74	9.669%	$205.8926	$205.89	$205.90	$205.90
7 purchase totals =	$1,117.08		$1,217.6132	$1,217.60	$1,217.60	$1,217.70