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	$9.57	5.105%	$10.0585	$10.06	$10.05	$10.10
Purchase #2	$130.32	11.398%	$145.1739	$145.17	$145.15	$145.20
Purchase #3	$221.71	5.429%	$233.7466	$233.75	$233.75	$233.70
Purchase #4	$23.92	10.206%	$26.3613	$26.36	$26.35	$26.40
Purchase #5	$91.54	4.246%	$95.4268	$95.43	$95.45	$95.40
Purchase #6	$35.97	6.412%	$38.2764	$38.28	$38.30	$38.30
Purchase #7	$105.39	12.282%	$118.334	$118.33	$118.35	$118.30
7 purchase totals =	$618.42		$667.3775	$667.38	$667.40	$667.40