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	$229.51	5.644%	$242.4635	$242.46	$242.45	$242.50
Purchase #2	$160.64	12.142%	$180.1449	$180.14	$180.15	$180.10
Purchase #3	$128.70	7.167%	$137.9239	$137.92	$137.90	$137.90
Purchase #4	$55.57	13.230%	$62.9219	$62.92	$62.90	$62.90
Purchase #5	$99.82	10.495%	$110.2961	$110.30	$110.30	$110.30
Purchase #6	$43.38	10.820%	$48.0737	$48.07	$48.05	$48.10
Purchase #7	$79.48	3.535%	$82.2896	$82.29	$82.30	$82.30
7 purchase totals =	$797.10		$864.1136	$864.10	$864.05	$864.10