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	$85.47	5.247%	$89.9546	$89.95	$89.95	$90.00
Purchase #2	$191.44	9.718%	$210.0441	$210.04	$210.05	$210.00
Purchase #3	$134.35	12.711%	$151.4272	$151.43	$151.45	$151.40
Purchase #4	$204.82	9.196%	$223.6552	$223.66	$223.65	$223.70
Purchase #5	$11.27	9.301%	$12.3182	$12.32	$12.30	$12.30
Purchase #6	$52.44	4.553%	$54.8276	$54.83	$54.85	$54.80
Purchase #7	$121.94	8.414%	$132.2	$132.20	$132.20	$132.20
7 purchase totals =	$801.73		$874.4269	$874.43	$874.45	$874.40