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	$185.92	12.854%	$209.8182	$209.82	$209.80	$209.80
Purchase #2	$46.62	9.211%	$50.9142	$50.91	$50.90	$50.90
Purchase #3	$172.78	13.220%	$195.6215	$195.62	$195.60	$195.60
Purchase #4	$156.54	12.813%	$176.5975	$176.60	$176.60	$176.60
Purchase #5	$11.40	9.281%	$12.458	$12.46	$12.45	$12.50
Purchase #6	$97.51	3.385%	$100.8107	$100.81	$100.80	$100.80
Purchase #7	$100.55	13.670%	$114.2952	$114.30	$114.30	$114.30
7 purchase totals =	$771.32		$860.5153	$860.52	$860.45	$860.50