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	$11.33	12.826%	$12.7832	$12.78	$12.80	$12.80
Purchase #2	$131.78	5.846%	$139.4839	$139.48	$139.50	$139.50
Purchase #3	$55.44	8.164%	$59.9661	$59.97	$59.95	$60.00
Purchase #4	$81.63	10.405%	$90.1236	$90.12	$90.10	$90.10
Purchase #5	$249.51	12.192%	$279.9303	$279.93	$279.95	$279.90
Purchase #6	$134.58	12.184%	$150.9772	$150.98	$151.00	$151.00
Purchase #7	$130.27	12.493%	$146.5446	$146.54	$146.55	$146.50
7 purchase totals =	$794.54		$879.8089	$879.80	$879.85	$879.80