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	$30.33	7.318%	$32.5495	$32.55	$32.55	$32.50
Purchase #2	$112.36	12.570%	$126.4837	$126.48	$126.50	$126.50
Purchase #3	$113.71	12.213%	$127.5974	$127.60	$127.60	$127.60
Purchase #4	$250.35	6.445%	$266.4851	$266.49	$266.50	$266.50
Purchase #5	$91.34	11.338%	$101.6961	$101.70	$101.70	$101.70
Purchase #6	$61.45	9.179%	$67.0905	$67.09	$67.10	$67.10
Purchase #7	$231.59	11.625%	$258.5123	$258.51	$258.50	$258.50
7 purchase totals =	$891.13		$980.4146	$980.42	$980.45	$980.40