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	$165.42	3.701%	$171.5422	$171.54	$171.55	$171.50
Purchase #2	$199.50	10.871%	$221.1876	$221.19	$221.20	$221.20
Purchase #3	$191.81	9.234%	$209.5217	$209.52	$209.50	$209.50
Purchase #4	$208.93	10.748%	$231.3858	$231.39	$231.40	$231.40
Purchase #5	$163.37	10.103%	$179.8753	$179.88	$179.90	$179.90
Purchase #6	$101.51	12.587%	$114.2871	$114.29	$114.30	$114.30
Purchase #7	$88.25	7.196%	$94.6005	$94.60	$94.60	$94.60
7 purchase totals =	$1,118.79		$1,222.4002	$1,222.41	$1,222.45	$1,222.40