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	$75.52	9.133%	$82.4172	$82.42	$82.40	$82.40
Purchase #2	$54.62	13.616%	$62.0571	$62.06	$62.05	$62.10
Purchase #3	$89.79	10.458%	$99.1802	$99.18	$99.20	$99.20
Purchase #4	$111.25	10.662%	$123.1115	$123.11	$123.10	$123.10
Purchase #5	$195.55	13.105%	$221.1768	$221.18	$221.20	$221.20
Purchase #6	$55.41	7.319%	$59.4655	$59.47	$59.45	$59.50
Purchase #7	$141.89	6.853%	$151.6137	$151.61	$151.60	$151.60
7 purchase totals =	$724.03		$799.0220	$799.03	$799.00	$799.10