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	$115.56	10.578%	$127.7839	$127.78	$127.80	$127.80
Purchase #2	$79.63	12.859%	$89.8696	$89.87	$89.85	$89.90
Purchase #3	$246.62	7.182%	$264.3322	$264.33	$264.35	$264.30
Purchase #4	$11.45	4.553%	$11.9713	$11.97	$11.95	$12.00
Purchase #5	$153.35	7.574%	$164.9647	$164.96	$164.95	$165.00
Purchase #6	$102.85	10.868%	$114.0277	$114.03	$114.05	$114.00
Purchase #7	$111.39	4.475%	$116.3747	$116.37	$116.35	$116.40
7 purchase totals =	$820.85		$889.3241	$889.31	$889.30	$889.40