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	$136.50	7.359%	$146.545	$146.55	$146.55	$146.50
Purchase #2	$174.98	12.233%	$196.3853	$196.39	$196.40	$196.40
Purchase #3	$35.53	11.437%	$39.5936	$39.59	$39.60	$39.60
Purchase #4	$38.31	4.545%	$40.0512	$40.05	$40.05	$40.10
Purchase #5	$211.96	5.271%	$223.1324	$223.13	$223.15	$223.10
Purchase #6	$216.67	6.425%	$230.591	$230.59	$230.60	$230.60
Purchase #7	$34.95	13.834%	$39.785	$39.79	$39.80	$39.80
7 purchase totals =	$848.90		$916.0835	$916.09	$916.15	$916.10