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	$231.70	8.282%	$250.8894	$250.89	$250.90	$250.90
Purchase #2	$159.59	8.838%	$173.6946	$173.69	$173.70	$173.70
Purchase #3	$234.41	13.244%	$265.4553	$265.46	$265.45	$265.50
Purchase #4	$218.85	10.513%	$241.8577	$241.86	$241.85	$241.90
Purchase #5	$132.80	13.144%	$150.2552	$150.26	$150.25	$150.30
Purchase #6	$38.40	9.720%	$42.1325	$42.13	$42.15	$42.10
Purchase #7	$80.33	8.350%	$87.0376	$87.04	$87.05	$87.00
7 purchase totals =	$1,096.08		$1,211.3223	$1,211.33	$1,211.35	$1,211.40