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	$58.73	12.632%	$66.1488	$66.15	$66.15	$66.10
Purchase #2	$206.80	7.648%	$222.6161	$222.62	$222.60	$222.60
Purchase #3	$163.55	6.484%	$174.1546	$174.15	$174.15	$174.20
Purchase #4	$177.26	3.514%	$183.4889	$183.49	$183.50	$183.50
Purchase #5	$87.41	5.153%	$91.9142	$91.91	$91.90	$91.90
Purchase #6	$108.73	7.550%	$116.9391	$116.94	$116.95	$116.90
Purchase #7	$137.89	10.467%	$152.3229	$152.32	$152.30	$152.30
7 purchase totals =	$940.37		$1,007.5846	$1,007.58	$1,007.55	$1,007.50