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	$27.92	4.609%	$29.2068	$29.21	$29.20	$29.20
Purchase #2	$51.58	9.150%	$56.2996	$56.30	$56.30	$56.30
Purchase #3	$173.64	6.767%	$185.3902	$185.39	$185.40	$185.40
Purchase #4	$34.27	5.145%	$36.0332	$36.03	$36.05	$36.00
Purchase #5	$183.78	4.188%	$191.4767	$191.48	$191.50	$191.50
Purchase #6	$123.72	12.757%	$139.503	$139.50	$139.50	$139.50
Purchase #7	$234.45	6.327%	$249.2837	$249.28	$249.30	$249.30
7 purchase totals =	$829.36		$887.1932	$887.19	$887.25	$887.20