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	$82.53	8.834%	$89.8207	$89.82	$89.80	$89.80
Purchase #2	$198.97	3.310%	$205.5559	$205.56	$205.55	$205.60
Purchase #3	$24.37	13.678%	$27.7033	$27.70	$27.70	$27.70
Purchase #4	$184.74	6.430%	$196.6188	$196.62	$196.60	$196.60
Purchase #5	$177.67	5.715%	$187.8238	$187.82	$187.80	$187.80
Purchase #6	$33.42	13.185%	$37.8264	$37.83	$37.85	$37.80
Purchase #7	$53.94	5.128%	$56.706	$56.71	$56.70	$56.70
7 purchase totals =	$755.64		$802.0549	$802.06	$802.00	$802.00