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	$113.73	9.267%	$124.2694	$124.27	$124.25	$124.30
Purchase #2	$238.72	9.757%	$262.0119	$262.01	$262.00	$262.00
Purchase #3	$18.73	6.223%	$19.8956	$19.90	$19.90	$19.90
Purchase #4	$81.40	11.449%	$90.7195	$90.72	$90.70	$90.70
Purchase #5	$200.72	10.127%	$221.0469	$221.05	$221.05	$221.00
Purchase #6	$145.55	3.584%	$150.7665	$150.77	$150.75	$150.80
Purchase #7	$39.69	4.756%	$41.5777	$41.58	$41.60	$41.60
7 purchase totals =	$838.54		$910.2875	$910.30	$910.25	$910.30