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	$155.85	10.692%	$172.5135	$172.51	$172.50	$172.50
Purchase #2	$50.48	3.259%	$52.1251	$52.13	$52.15	$52.10
Purchase #3	$141.91	13.373%	$160.8876	$160.89	$160.90	$160.90
Purchase #4	$119.67	10.805%	$132.6003	$132.60	$132.60	$132.60
Purchase #5	$243.28	12.510%	$273.7143	$273.71	$273.70	$273.70
Purchase #6	$19.55	8.873%	$21.2847	$21.28	$21.30	$21.30
Purchase #7	$102.85	3.267%	$106.2101	$106.21	$106.20	$106.20
7 purchase totals =	$833.59		$919.3356	$919.33	$919.35	$919.30