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	$71.66	9.509%	$78.4741	$78.47	$78.45	$78.50
Purchase #2	$70.96	8.455%	$76.9597	$76.96	$76.95	$77.00
Purchase #3	$159.67	12.131%	$179.0396	$179.04	$179.05	$179.00
Purchase #4	$220.84	5.644%	$233.3042	$233.30	$233.30	$233.30
Purchase #5	$174.83	5.326%	$184.1414	$184.14	$184.15	$184.10
Purchase #6	$63.78	10.546%	$70.5062	$70.51	$70.50	$70.50
Purchase #7	$82.74	3.773%	$85.8618	$85.86	$85.85	$85.90
7 purchase totals =	$844.48		$908.2870	$908.28	$908.25	$908.30