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	$33.77	4.812%	$35.395	$35.40	$35.40	$35.40
Purchase #2	$228.95	11.221%	$254.6405	$254.64	$254.65	$254.60
Purchase #3	$11.98	12.604%	$13.49	$13.49	$13.50	$13.50
Purchase #4	$72.29	8.731%	$78.6016	$78.60	$78.60	$78.60
Purchase #5	$46.65	10.742%	$51.6611	$51.66	$51.65	$51.70
Purchase #6	$54.94	10.458%	$60.6856	$60.69	$60.70	$60.70
Purchase #7	$83.97	7.327%	$90.1225	$90.12	$90.10	$90.10
7 purchase totals =	$532.55		$584.5963	$584.60	$584.60	$584.60