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	$220.52	4.126%	$229.6187	$229.62	$229.60	$229.60
Purchase #2	$69.46	13.464%	$78.8121	$78.81	$78.80	$78.80
Purchase #3	$164.86	12.483%	$185.4395	$185.44	$185.45	$185.40
Purchase #4	$80.30	11.230%	$89.3177	$89.32	$89.30	$89.30
Purchase #5	$87.84	13.695%	$99.8697	$99.87	$99.85	$99.90
Purchase #6	$18.76	10.779%	$20.7821	$20.78	$20.80	$20.80
Purchase #7	$205.80	10.378%	$227.1579	$227.16	$227.15	$227.20
7 purchase totals =	$847.54		$930.9977	$931.00	$930.95	$931.00