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	$161.78	4.210%	$168.5909	$168.59	$168.60	$168.60
Purchase #2	$227.77	12.207%	$255.5739	$255.57	$255.55	$255.60
Purchase #3	$232.76	7.688%	$250.6546	$250.65	$250.65	$250.70
Purchase #4	$54.42	12.248%	$61.0854	$61.09	$61.10	$61.10
Purchase #5	$167.85	10.570%	$185.5917	$185.59	$185.60	$185.60
Purchase #6	$113.45	12.851%	$128.0295	$128.03	$128.05	$128.00
Purchase #7	$44.90	12.274%	$50.411	$50.41	$50.40	$50.40
7 purchase totals =	$1,002.93		$1,099.9370	$1,099.93	$1,099.95	$1,100.00