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	$167.59	10.491%	$185.1719	$185.17	$185.15	$185.20
Purchase #2	$138.82	3.528%	$143.7176	$143.72	$143.70	$143.70
Purchase #3	$190.89	7.844%	$205.8634	$205.86	$205.85	$205.90
Purchase #4	$96.73	3.663%	$100.2732	$100.27	$100.25	$100.30
Purchase #5	$72.32	6.326%	$76.895	$76.90	$76.90	$76.90
Purchase #6	$40.25	13.778%	$45.7956	$45.80	$45.80	$45.80
Purchase #7	$77.58	5.210%	$81.6219	$81.62	$81.60	$81.60
7 purchase totals =	$784.18		$839.3386	$839.34	$839.25	$839.40