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	$154.29	4.678%	$161.5077	$161.51	$161.50	$161.50
Purchase #2	$79.89	6.472%	$85.0605	$85.06	$85.05	$85.10
Purchase #3	$208.74	6.861%	$223.0617	$223.06	$223.05	$223.10
Purchase #4	$147.51	7.676%	$158.8329	$158.83	$158.85	$158.80
Purchase #5	$26.81	4.407%	$27.9915	$27.99	$28.00	$28.00
Purchase #6	$102.65	9.498%	$112.3997	$112.40	$112.40	$112.40
Purchase #7	$13.56	13.459%	$15.385	$15.39	$15.40	$15.40
7 purchase totals =	$733.45		$784.2390	$784.24	$784.25	$784.30