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	$35.55	4.188%	$37.0388	$37.04	$37.05	$37.00
Purchase #2	$51.58	3.588%	$53.4307	$53.43	$53.45	$53.40
Purchase #3	$79.80	4.735%	$83.5785	$83.58	$83.60	$83.60
Purchase #4	$97.97	5.395%	$103.2555	$103.26	$103.25	$103.30
Purchase #5	$145.26	5.703%	$153.5442	$153.54	$153.55	$153.50
Purchase #6	$27.75	12.292%	$31.161	$31.16	$31.15	$31.20
Purchase #7	$170.40	4.706%	$178.419	$178.42	$178.40	$178.40
7 purchase totals =	$608.31		$640.4277	$640.43	$640.45	$640.40