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	$78.91	12.578%	$88.8353	$88.84	$88.85	$88.80
Purchase #2	$247.33	6.219%	$262.7115	$262.71	$262.70	$262.70
Purchase #3	$48.41	6.605%	$51.6075	$51.61	$51.60	$51.60
Purchase #4	$7.28	4.459%	$7.6046	$7.60	$7.60	$7.60
Purchase #5	$57.71	13.530%	$65.5182	$65.52	$65.50	$65.50
Purchase #6	$156.58	7.577%	$168.4441	$168.44	$168.45	$168.40
Purchase #7	$128.66	8.227%	$139.2449	$139.24	$139.25	$139.20
7 purchase totals =	$724.88		$783.9661	$783.96	$783.95	$783.80