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	$50.25	12.637%	$56.6001	$56.60	$56.60	$56.60
Purchase #2	$92.38	8.247%	$99.9986	$100.00	$100.00	$100.00
Purchase #3	$202.31	6.786%	$216.0388	$216.04	$216.05	$216.00
Purchase #4	$93.62	6.631%	$99.8279	$99.83	$99.85	$99.80
Purchase #5	$151.55	13.537%	$172.0653	$172.07	$172.05	$172.10
Purchase #6	$38.89	4.653%	$40.6996	$40.70	$40.70	$40.70
Purchase #7	$124.96	13.285%	$141.5609	$141.56	$141.55	$141.60
7 purchase totals =	$753.96		$826.7912	$826.80	$826.80	$826.80