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	$171.94	3.598%	$178.1264	$178.13	$178.15	$178.10
Purchase #2	$151.75	5.646%	$160.3178	$160.32	$160.30	$160.30
Purchase #3	$90.81	9.165%	$99.1327	$99.13	$99.15	$99.10
Purchase #4	$57.72	9.647%	$63.2882	$63.29	$63.30	$63.30
Purchase #5	$8.62	7.250%	$9.245	$9.25	$9.25	$9.20
Purchase #6	$101.38	11.321%	$112.8572	$112.86	$112.85	$112.90
Purchase #7	$111.71	11.105%	$124.1154	$124.12	$124.10	$124.10
7 purchase totals =	$693.93		$747.0827	$747.10	$747.10	$747.00