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	$216.74	6.519%	$230.8693	$230.87	$230.85	$230.90
Purchase #2	$93.59	11.643%	$104.4867	$104.49	$104.50	$104.50
Purchase #3	$151.32	3.699%	$156.9173	$156.92	$156.90	$156.90
Purchase #4	$46.53	3.752%	$48.2758	$48.28	$48.30	$48.30
Purchase #5	$188.50	8.277%	$204.1021	$204.10	$204.10	$204.10
Purchase #6	$155.54	5.480%	$164.0636	$164.06	$164.05	$164.10
Purchase #7	$79.48	13.603%	$90.2917	$90.29	$90.30	$90.30
7 purchase totals =	$931.70		$999.0065	$999.01	$999.00	$999.10