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	$90.93	4.228%	$94.7745	$94.77	$94.75	$94.80
Purchase #2	$178.43	6.526%	$190.0743	$190.07	$190.05	$190.10
Purchase #3	$95.67	4.230%	$99.7168	$99.72	$99.70	$99.70
Purchase #4	$43.32	5.280%	$45.6073	$45.61	$45.60	$45.60
Purchase #5	$207.91	10.197%	$229.1106	$229.11	$229.10	$229.10
Purchase #6	$12.29	6.829%	$13.1293	$13.13	$13.15	$13.10
Purchase #7	$219.90	9.169%	$240.0626	$240.06	$240.05	$240.10
7 purchase totals =	$848.45		$912.4754	$912.47	$912.40	$912.50