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	$17.94	11.839%	$20.0639	$20.06	$20.05	$20.10
Purchase #2	$88.62	11.242%	$98.5827	$98.58	$98.60	$98.60
Purchase #3	$148.39	8.160%	$160.4986	$160.50	$160.50	$160.50
Purchase #4	$104.66	13.111%	$118.382	$118.38	$118.40	$118.40
Purchase #5	$123.88	13.502%	$140.6063	$140.61	$140.60	$140.60
Purchase #6	$135.39	7.717%	$145.838	$145.84	$145.85	$145.80
Purchase #7	$75.83	3.227%	$78.277	$78.28	$78.30	$78.30
7 purchase totals =	$694.71		$762.2485	$762.25	$762.30	$762.30