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	$17.71	12.716%	$19.962	$19.96	$19.95	$20.00
Purchase #2	$80.61	12.402%	$90.6073	$90.61	$90.60	$90.60
Purchase #3	$105.50	8.819%	$114.804	$114.80	$114.80	$114.80
Purchase #4	$111.98	11.298%	$124.6315	$124.63	$124.65	$124.60
Purchase #5	$149.30	11.216%	$166.0455	$166.05	$166.05	$166.00
Purchase #6	$128.77	11.454%	$143.5193	$143.52	$143.50	$143.50
Purchase #7	$145.71	11.600%	$162.6124	$162.61	$162.60	$162.60
7 purchase totals =	$739.58		$822.1820	$822.18	$822.15	$822.10