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	$134.67	6.280%	$143.1273	$143.13	$143.15	$143.10
Purchase #2	$87.66	3.737%	$90.9359	$90.94	$90.95	$90.90
Purchase #3	$181.44	4.424%	$189.4669	$189.47	$189.45	$189.50
Purchase #4	$103.41	8.529%	$112.2298	$112.23	$112.25	$112.20
Purchase #5	$155.59	6.344%	$165.4606	$165.46	$165.45	$165.50
Purchase #6	$111.81	5.329%	$117.7684	$117.77	$117.75	$117.80
Purchase #7	$56.63	12.129%	$63.4987	$63.50	$63.50	$63.50
7 purchase totals =	$831.21		$882.4876	$882.50	$882.50	$882.50