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	$37.59	3.271%	$38.8196	$38.82	$38.80	$38.80
Purchase #2	$86.34	12.800%	$97.3915	$97.39	$97.40	$97.40
Purchase #3	$29.87	5.446%	$31.4967	$31.50	$31.50	$31.50
Purchase #4	$122.36	12.828%	$138.0563	$138.06	$138.05	$138.10
Purchase #5	$84.78	11.263%	$94.3288	$94.33	$94.35	$94.30
Purchase #6	$113.33	12.501%	$127.4974	$127.50	$127.50	$127.50
Purchase #7	$18.96	4.781%	$19.8665	$19.87	$19.85	$19.90
7 purchase totals =	$493.23		$547.4568	$547.47	$547.45	$547.50