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	$145.66	10.565%	$161.049	$161.05	$161.05	$161.00
Purchase #2	$49.65	13.234%	$56.2207	$56.22	$56.20	$56.20
Purchase #3	$154.81	10.625%	$171.2586	$171.26	$171.25	$171.30
Purchase #4	$50.43	5.556%	$53.2319	$53.23	$53.25	$53.20
Purchase #5	$40.38	8.714%	$43.8987	$43.90	$43.90	$43.90
Purchase #6	$30.71	13.514%	$34.8601	$34.86	$34.85	$34.90
Purchase #7	$70.69	13.856%	$80.4848	$80.48	$80.50	$80.50
7 purchase totals =	$542.33		$601.0038	$601.00	$601.00	$601.00