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	$200.60	8.762%	$218.1766	$218.18	$218.20	$218.20
Purchase #2	$60.60	9.822%	$66.5521	$66.55	$66.55	$66.60
Purchase #3	$132.61	8.868%	$144.3699	$144.37	$144.35	$144.40
Purchase #4	$71.43	3.346%	$73.82	$73.82	$73.80	$73.80
Purchase #5	$72.56	7.736%	$78.1732	$78.17	$78.15	$78.20
Purchase #6	$178.89	3.643%	$185.407	$185.41	$185.40	$185.40
Purchase #7	$41.42	13.666%	$47.0805	$47.08	$47.10	$47.10
7 purchase totals =	$758.11		$813.5793	$813.58	$813.55	$813.70