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	$158.70	12.468%	$178.4867	$178.49	$178.50	$178.50
Purchase #2	$79.46	10.366%	$87.6968	$87.70	$87.70	$87.70
Purchase #3	$37.50	5.270%	$39.4763	$39.48	$39.50	$39.50
Purchase #4	$57.83	3.554%	$59.8853	$59.89	$59.90	$59.90
Purchase #5	$148.78	8.121%	$160.8624	$160.86	$160.85	$160.90
Purchase #6	$98.93	12.579%	$111.3744	$111.37	$111.35	$111.40
Purchase #7	$36.90	10.675%	$40.8391	$40.84	$40.85	$40.80
7 purchase totals =	$618.10		$678.6210	$678.63	$678.65	$678.70