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	$110.33	9.349%	$120.6448	$120.64	$120.65	$120.60
Purchase #2	$149.83	4.468%	$156.5244	$156.52	$156.50	$156.50
Purchase #3	$38.46	10.559%	$42.521	$42.52	$42.50	$42.50
Purchase #4	$81.50	10.407%	$89.9817	$89.98	$90.00	$90.00
Purchase #5	$98.38	4.178%	$102.4903	$102.49	$102.50	$102.50
Purchase #6	$76.51	5.458%	$80.6859	$80.69	$80.70	$80.70
Purchase #7	$56.65	12.587%	$63.7805	$63.78	$63.80	$63.80
7 purchase totals =	$611.66		$656.6286	$656.62	$656.65	$656.60