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	$49.57	13.822%	$56.4216	$56.42	$56.40	$56.40
Purchase #2	$29.28	4.436%	$30.5789	$30.58	$30.60	$30.60
Purchase #3	$101.53	9.627%	$111.3043	$111.30	$111.30	$111.30
Purchase #4	$73.38	9.656%	$80.4656	$80.47	$80.45	$80.50
Purchase #5	$205.27	11.850%	$229.5945	$229.59	$229.60	$229.60
Purchase #6	$188.29	12.561%	$211.9411	$211.94	$211.95	$211.90
Purchase #7	$37.54	6.730%	$40.0664	$40.07	$40.05	$40.10
7 purchase totals =	$684.86		$760.3724	$760.37	$760.35	$760.40