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	$143.93	5.532%	$151.8922	$151.89	$151.90	$151.90
Purchase #2	$209.86	11.190%	$233.3433	$233.34	$233.35	$233.30
Purchase #3	$117.74	12.273%	$132.1902	$132.19	$132.20	$132.20
Purchase #4	$194.66	4.543%	$203.5034	$203.50	$203.50	$203.50
Purchase #5	$12.28	8.726%	$13.3516	$13.35	$13.35	$13.40
Purchase #6	$176.27	12.613%	$198.5029	$198.50	$198.50	$198.50
Purchase #7	$61.74	8.602%	$67.0509	$67.05	$67.05	$67.10
7 purchase totals =	$916.48		$999.8345	$999.82	$999.85	$999.90