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	$19.25	11.555%	$21.4743	$21.47	$21.45	$21.50
Purchase #2	$114.90	8.456%	$124.6159	$124.62	$124.60	$124.60
Purchase #3	$244.98	12.222%	$274.9215	$274.92	$274.90	$274.90
Purchase #4	$31.45	4.624%	$32.9042	$32.90	$32.90	$32.90
Purchase #5	$75.34	4.335%	$78.606	$78.61	$78.60	$78.60
Purchase #6	$232.76	11.261%	$258.9711	$258.97	$258.95	$259.00
Purchase #7	$170.39	7.379%	$182.9631	$182.96	$182.95	$183.00
7 purchase totals =	$889.07		$974.4561	$974.45	$974.35	$974.50