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	$204.56	13.636%	$232.4538	$232.45	$232.45	$232.50
Purchase #2	$127.29	9.140%	$138.9243	$138.92	$138.90	$138.90
Purchase #3	$19.33	13.198%	$21.8812	$21.88	$21.90	$21.90
Purchase #4	$65.69	7.327%	$70.5031	$70.50	$70.50	$70.50
Purchase #5	$167.73	10.331%	$185.0582	$185.06	$185.05	$185.10
Purchase #6	$211.49	4.673%	$221.3729	$221.37	$221.35	$221.40
Purchase #7	$52.44	12.652%	$59.0747	$59.07	$59.05	$59.10
7 purchase totals =	$848.53		$929.2682	$929.25	$929.20	$929.40