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	$38.31	10.280%	$42.2483	$42.25	$42.25	$42.20
Purchase #2	$106.34	6.430%	$113.1777	$113.18	$113.20	$113.20
Purchase #3	$73.62	4.785%	$77.1427	$77.14	$77.15	$77.10
Purchase #4	$142.83	3.662%	$148.0604	$148.06	$148.05	$148.10
Purchase #5	$132.49	8.632%	$143.9265	$143.93	$143.95	$143.90
Purchase #6	$89.56	6.183%	$95.0975	$95.10	$95.10	$95.10
Purchase #7	$151.67	5.434%	$159.9117	$159.91	$159.90	$159.90
7 purchase totals =	$734.82		$779.5648	$779.57	$779.60	$779.50