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	$60.63	10.169%	$66.7955	$66.80	$66.80	$66.80
Purchase #2	$68.36	13.304%	$77.4546	$77.45	$77.45	$77.50
Purchase #3	$178.54	13.816%	$203.2071	$203.21	$203.20	$203.20
Purchase #4	$95.25	10.684%	$105.4265	$105.43	$105.45	$105.40
Purchase #5	$56.71	12.339%	$63.7074	$63.71	$63.70	$63.70
Purchase #6	$64.37	11.697%	$71.8994	$71.90	$71.90	$71.90
Purchase #7	$36.71	12.657%	$41.3564	$41.36	$41.35	$41.40
7 purchase totals =	$560.57		$629.8469	$629.86	$629.85	$629.90