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	$130.76	4.794%	$137.0286	$137.03	$137.05	$137.00
Purchase #2	$138.89	13.229%	$157.2638	$157.26	$157.25	$157.30
Purchase #3	$148.78	8.361%	$161.2195	$161.22	$161.20	$161.20
Purchase #4	$75.89	3.850%	$78.8118	$78.81	$78.80	$78.80
Purchase #5	$148.62	9.621%	$162.9187	$162.92	$162.90	$162.90
Purchase #6	$30.28	6.596%	$32.2773	$32.28	$32.30	$32.30
Purchase #7	$81.87	11.259%	$91.0877	$91.09	$91.10	$91.10
7 purchase totals =	$755.09		$820.6074	$820.61	$820.60	$820.60