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	$45.67	7.385%	$49.0427	$49.04	$49.05	$49.00
Purchase #2	$228.86	9.350%	$250.2584	$250.26	$250.25	$250.30
Purchase #3	$38.41	9.554%	$42.0797	$42.08	$42.10	$42.10
Purchase #4	$88.71	13.201%	$100.4206	$100.42	$100.40	$100.40
Purchase #5	$156.93	4.241%	$163.5854	$163.59	$163.60	$163.60
Purchase #6	$85.39	4.682%	$89.388	$89.39	$89.40	$89.40
Purchase #7	$66.82	5.680%	$70.6154	$70.62	$70.60	$70.60
7 purchase totals =	$710.79		$765.3902	$765.40	$765.40	$765.40