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	$100.37	11.436%	$111.8483	$111.85	$111.85	$111.80
Purchase #2	$249.90	5.833%	$264.4767	$264.48	$264.50	$264.50
Purchase #3	$131.26	7.462%	$141.0546	$141.05	$141.05	$141.10
Purchase #4	$68.64	7.564%	$73.8319	$73.83	$73.85	$73.80
Purchase #5	$144.64	6.349%	$153.8232	$153.82	$153.80	$153.80
Purchase #6	$155.58	9.873%	$170.9404	$170.94	$170.95	$170.90
Purchase #7	$167.74	3.308%	$173.2888	$173.29	$173.30	$173.30
7 purchase totals =	$1,018.13		$1,089.2639	$1,089.26	$1,089.30	$1,089.20