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	$249.57	6.769%	$266.4634	$266.46	$266.45	$266.50
Purchase #2	$54.60	3.278%	$56.3898	$56.39	$56.40	$56.40
Purchase #3	$130.79	12.141%	$146.6692	$146.67	$146.65	$146.70
Purchase #4	$64.53	12.741%	$72.7518	$72.75	$72.75	$72.80
Purchase #5	$20.87	3.159%	$21.5293	$21.53	$21.55	$21.50
Purchase #6	$59.88	11.164%	$66.565	$66.57	$66.55	$66.60
Purchase #7	$169.38	11.300%	$188.5199	$188.52	$188.50	$188.50
7 purchase totals =	$749.62		$818.8884	$818.89	$818.85	$819.00