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	$65.67	4.408%	$68.5647	$68.56	$68.55	$68.60
Purchase #2	$40.65	12.142%	$45.5857	$45.59	$45.60	$45.60
Purchase #3	$131.90	6.160%	$140.025	$140.03	$140.05	$140.00
Purchase #4	$142.42	12.510%	$160.2367	$160.24	$160.25	$160.20
Purchase #5	$89.90	4.698%	$94.1235	$94.12	$94.10	$94.10
Purchase #6	$42.27	3.651%	$43.8133	$43.81	$43.80	$43.80
Purchase #7	$26.62	6.499%	$28.35	$28.35	$28.35	$28.40
7 purchase totals =	$539.43		$580.6989	$580.70	$580.70	$580.70