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	$89.64	12.114%	$100.499	$100.50	$100.50	$100.50
Purchase #2	$168.26	6.566%	$179.308	$179.31	$179.30	$179.30
Purchase #3	$33.39	13.352%	$37.8482	$37.85	$37.85	$37.80
Purchase #4	$204.78	6.390%	$217.8654	$217.87	$217.85	$217.90
Purchase #5	$73.90	3.211%	$76.2729	$76.27	$76.25	$76.30
Purchase #6	$107.95	12.271%	$121.1965	$121.20	$121.20	$121.20
Purchase #7	$194.35	12.402%	$218.4533	$218.45	$218.45	$218.50
7 purchase totals =	$872.27		$951.4433	$951.45	$951.40	$951.50