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	$150.54	3.254%	$155.4386	$155.44	$155.45	$155.40
Purchase #2	$30.77	6.785%	$32.8577	$32.86	$32.85	$32.90
Purchase #3	$138.47	3.721%	$143.6225	$143.62	$143.60	$143.60
Purchase #4	$117.88	8.217%	$127.5662	$127.57	$127.55	$127.60
Purchase #5	$234.49	3.388%	$242.4345	$242.43	$242.45	$242.40
Purchase #6	$42.58	5.269%	$44.8235	$44.82	$44.80	$44.80
Purchase #7	$129.48	8.529%	$140.5233	$140.52	$140.50	$140.50
7 purchase totals =	$844.21		$887.2663	$887.26	$887.20	$887.20