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	$31.40	7.429%	$33.7327	$33.73	$33.75	$33.70
Purchase #2	$56.46	5.566%	$59.6026	$59.60	$59.60	$59.60
Purchase #3	$151.52	10.516%	$167.4538	$167.45	$167.45	$167.50
Purchase #4	$123.88	3.705%	$128.4698	$128.47	$128.45	$128.50
Purchase #5	$31.89	5.185%	$33.5435	$33.54	$33.55	$33.50
Purchase #6	$200.77	11.756%	$224.3725	$224.37	$224.35	$224.40
Purchase #7	$250.67	13.434%	$284.345	$284.35	$284.35	$284.30
7 purchase totals =	$846.59		$931.5199	$931.51	$931.50	$931.50