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	$56.98	10.256%	$62.8239	$62.82	$62.80	$62.80
Purchase #2	$35.84	8.555%	$38.9061	$38.91	$38.90	$38.90
Purchase #3	$13.53	12.156%	$15.1747	$15.17	$15.15	$15.20
Purchase #4	$228.45	8.826%	$248.613	$248.61	$248.60	$248.60
Purchase #5	$90.45	10.794%	$100.2132	$100.21	$100.20	$100.20
Purchase #6	$241.73	6.757%	$258.0637	$258.06	$258.05	$258.10
Purchase #7	$87.35	5.601%	$92.2425	$92.24	$92.25	$92.20
7 purchase totals =	$754.33		$816.0371	$816.02	$815.95	$816.00