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	$35.96	13.653%	$40.8696	$40.87	$40.85	$40.90
Purchase #2	$188.69	9.486%	$206.5891	$206.59	$206.60	$206.60
Purchase #3	$130.74	5.833%	$138.3661	$138.37	$138.35	$138.40
Purchase #4	$140.31	3.249%	$144.8687	$144.87	$144.85	$144.90
Purchase #5	$38.37	8.422%	$41.6015	$41.60	$41.60	$41.60
Purchase #6	$14.82	7.234%	$15.8921	$15.89	$15.90	$15.90
Purchase #7	$53.42	13.710%	$60.7439	$60.74	$60.75	$60.70
7 purchase totals =	$602.31		$648.9310	$648.93	$648.90	$649.00