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	$31.33	4.195%	$32.6443	$32.64	$32.65	$32.60
Purchase #2	$29.43	3.205%	$30.3732	$30.37	$30.35	$30.40
Purchase #3	$37.29	11.226%	$41.4762	$41.48	$41.50	$41.50
Purchase #4	$97.56	12.212%	$109.474	$109.47	$109.45	$109.50
Purchase #5	$104.33	6.484%	$111.0948	$111.09	$111.10	$111.10
Purchase #6	$223.83	4.169%	$233.1615	$233.16	$233.15	$233.20
Purchase #7	$94.47	9.173%	$103.1357	$103.14	$103.15	$103.10
7 purchase totals =	$618.24		$661.3597	$661.35	$661.35	$661.40