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	$121.33	5.782%	$128.3453	$128.35	$128.35	$128.30
Purchase #2	$155.51	7.724%	$167.5216	$167.52	$167.50	$167.50
Purchase #3	$5.48	13.580%	$6.2242	$6.22	$6.20	$6.20
Purchase #4	$219.83	6.734%	$234.6334	$234.63	$234.65	$234.60
Purchase #5	$99.82	11.240%	$111.0398	$111.04	$111.05	$111.00
Purchase #6	$218.78	4.484%	$228.5901	$228.59	$228.60	$228.60
Purchase #7	$109.53	6.340%	$116.4742	$116.47	$116.45	$116.50
7 purchase totals =	$930.28		$992.8286	$992.82	$992.80	$992.70