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	$56.45	5.289%	$59.4356	$59.44	$59.45	$59.40
Purchase #2	$28.97	8.631%	$31.4704	$31.47	$31.45	$31.50
Purchase #3	$103.87	6.635%	$110.7618	$110.76	$110.75	$110.80
Purchase #4	$217.70	8.215%	$235.5841	$235.58	$235.60	$235.60
Purchase #5	$127.29	3.463%	$131.6981	$131.70	$131.70	$131.70
Purchase #6	$169.81	9.298%	$185.5989	$185.60	$185.60	$185.60
Purchase #7	$167.79	7.345%	$180.1142	$180.11	$180.10	$180.10
7 purchase totals =	$871.88		$934.6631	$934.66	$934.65	$934.70