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	$18.40	6.524%	$19.6004	$19.60	$19.60	$19.60
Purchase #2	$151.52	13.756%	$172.3631	$172.36	$172.35	$172.40
Purchase #3	$61.78	8.695%	$67.1518	$67.15	$67.15	$67.20
Purchase #4	$209.67	3.604%	$217.2265	$217.23	$217.25	$217.20
Purchase #5	$234.56	9.207%	$256.1559	$256.16	$256.15	$256.20
Purchase #6	$181.29	3.258%	$187.1964	$187.20	$187.20	$187.20
Purchase #7	$74.49	5.766%	$78.7851	$78.79	$78.80	$78.80
7 purchase totals =	$931.71		$998.4792	$998.49	$998.50	$998.60