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	$113.51	8.471%	$123.1254	$123.13	$123.15	$123.10
Purchase #2	$55.78	13.670%	$63.4051	$63.41	$63.40	$63.40
Purchase #3	$22.72	3.103%	$23.425	$23.43	$23.45	$23.40
Purchase #4	$211.35	13.448%	$239.7723	$239.77	$239.75	$239.80
Purchase #5	$16.73	10.242%	$18.4435	$18.44	$18.45	$18.40
Purchase #6	$69.84	12.225%	$78.3779	$78.38	$78.40	$78.40
Purchase #7	$90.25	5.865%	$95.5432	$95.54	$95.55	$95.50
7 purchase totals =	$580.18		$642.0924	$642.10	$642.15	$642.00