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	$150.78	4.351%	$157.3404	$157.34	$157.35	$157.30
Purchase #2	$103.73	7.709%	$111.7265	$111.73	$111.75	$111.70
Purchase #3	$97.64	6.225%	$103.7181	$103.72	$103.70	$103.70
Purchase #4	$34.66	5.669%	$36.6249	$36.62	$36.60	$36.60
Purchase #5	$230.29	5.645%	$243.2899	$243.29	$243.30	$243.30
Purchase #6	$38.59	5.238%	$40.6113	$40.61	$40.60	$40.60
Purchase #7	$168.50	12.873%	$190.191	$190.19	$190.20	$190.20
7 purchase totals =	$824.19		$883.5021	$883.50	$883.50	$883.40