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	$94.58	6.221%	$100.4638	$100.46	$100.45	$100.50
Purchase #2	$250.57	12.342%	$281.4953	$281.50	$281.50	$281.50
Purchase #3	$61.46	5.584%	$64.8919	$64.89	$64.90	$64.90
Purchase #4	$121.99	13.353%	$138.2793	$138.28	$138.30	$138.30
Purchase #5	$50.40	8.112%	$54.4884	$54.49	$54.50	$54.50
Purchase #6	$134.97	3.560%	$139.7749	$139.77	$139.75	$139.80
Purchase #7	$102.88	13.583%	$116.8542	$116.85	$116.85	$116.90
7 purchase totals =	$816.85		$896.2478	$896.24	$896.25	$896.40