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	$59.77	9.781%	$65.6161	$65.62	$65.60	$65.60
Purchase #2	$51.79	4.751%	$54.2505	$54.25	$54.25	$54.30
Purchase #3	$131.62	4.871%	$138.0312	$138.03	$138.05	$138.00
Purchase #4	$120.89	3.335%	$124.9217	$124.92	$124.90	$124.90
Purchase #5	$19.85	11.348%	$22.1026	$22.10	$22.10	$22.10
Purchase #6	$103.90	10.260%	$114.5601	$114.56	$114.55	$114.60
Purchase #7	$84.54	5.793%	$89.4374	$89.44	$89.45	$89.40
7 purchase totals =	$572.36		$608.9196	$608.92	$608.90	$608.90