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	$227.69	10.363%	$251.2855	$251.29	$251.30	$251.30
Purchase #2	$51.38	4.495%	$53.6895	$53.69	$53.70	$53.70
Purchase #3	$29.69	10.164%	$32.7077	$32.71	$32.70	$32.70
Purchase #4	$212.61	7.184%	$227.8839	$227.88	$227.90	$227.90
Purchase #5	$70.81	11.263%	$78.7853	$78.79	$78.80	$78.80
Purchase #6	$150.39	11.373%	$167.4939	$167.49	$167.50	$167.50
Purchase #7	$94.47	3.656%	$97.9238	$97.92	$97.90	$97.90
7 purchase totals =	$837.04		$909.7696	$909.77	$909.80	$909.80