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	$174.72	12.444%	$196.4622	$196.46	$196.45	$196.50
Purchase #2	$131.56	11.146%	$146.2237	$146.22	$146.20	$146.20
Purchase #3	$78.92	13.587%	$89.6429	$89.64	$89.65	$89.60
Purchase #4	$146.53	11.602%	$163.5304	$163.53	$163.55	$163.50
Purchase #5	$49.76	8.785%	$54.1314	$54.13	$54.15	$54.10
Purchase #6	$11.54	12.631%	$12.9976	$13.00	$13.00	$13.00
Purchase #7	$196.51	13.121%	$222.2941	$222.29	$222.30	$222.30
7 purchase totals =	$789.54		$885.2823	$885.27	$885.30	$885.20