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	$144.89	12.154%	$162.4999	$162.50	$162.50	$162.50
Purchase #2	$77.33	12.114%	$86.6978	$86.70	$86.70	$86.70
Purchase #3	$248.45	5.119%	$261.1682	$261.17	$261.15	$261.20
Purchase #4	$29.96	10.743%	$33.1786	$33.18	$33.20	$33.20
Purchase #5	$162.74	10.386%	$179.6422	$179.64	$179.65	$179.60
Purchase #6	$82.68	5.822%	$87.4936	$87.49	$87.50	$87.50
Purchase #7	$52.32	13.798%	$59.5391	$59.54	$59.55	$59.50
7 purchase totals =	$798.37		$870.2194	$870.22	$870.25	$870.20