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	$99.84	9.816%	$109.6403	$109.64	$109.65	$109.60
Purchase #2	$51.56	7.595%	$55.476	$55.48	$55.50	$55.50
Purchase #3	$169.37	10.778%	$187.6247	$187.62	$187.60	$187.60
Purchase #4	$47.52	3.570%	$49.2165	$49.22	$49.20	$49.20
Purchase #5	$163.30	3.144%	$168.4342	$168.43	$168.45	$168.40
Purchase #6	$191.47	10.534%	$211.6394	$211.64	$211.65	$211.60
Purchase #7	$191.39	4.544%	$200.0868	$200.09	$200.10	$200.10
7 purchase totals =	$914.45		$982.1179	$982.12	$982.15	$982.00