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	$61.91	5.259%	$65.1658	$65.17	$65.15	$65.20
Purchase #2	$84.98	12.329%	$95.4572	$95.46	$95.45	$95.50
Purchase #3	$142.47	6.363%	$151.5354	$151.54	$151.55	$151.50
Purchase #4	$25.95	9.616%	$28.4454	$28.45	$28.45	$28.40
Purchase #5	$109.61	12.171%	$122.9506	$122.95	$122.95	$123.00
Purchase #6	$39.59	8.262%	$42.8609	$42.86	$42.85	$42.90
Purchase #7	$185.65	3.646%	$192.4188	$192.42	$192.40	$192.40
7 purchase totals =	$650.16		$698.8341	$698.85	$698.80	$698.90