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	$82.59	8.842%	$89.8926	$89.89	$89.90	$89.90
Purchase #2	$130.96	4.254%	$136.531	$136.53	$136.55	$136.50
Purchase #3	$23.65	4.841%	$24.7949	$24.79	$24.80	$24.80
Purchase #4	$56.45	5.162%	$59.3639	$59.36	$59.35	$59.40
Purchase #5	$148.53	13.697%	$168.8742	$168.87	$168.85	$168.90
Purchase #6	$29.60	9.806%	$32.5026	$32.50	$32.50	$32.50
Purchase #7	$105.96	6.701%	$113.0604	$113.06	$113.05	$113.10
7 purchase totals =	$577.74		$625.0196	$625.00	$625.00	$625.10