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	$53.70	7.305%	$57.6228	$57.62	$57.60	$57.60
Purchase #2	$129.46	10.231%	$142.7051	$142.71	$142.70	$142.70
Purchase #3	$46.42	8.671%	$50.4451	$50.45	$50.45	$50.40
Purchase #4	$24.51	5.770%	$25.9242	$25.92	$25.90	$25.90
Purchase #5	$90.69	11.286%	$100.9253	$100.93	$100.95	$100.90
Purchase #6	$241.26	13.352%	$273.473	$273.47	$273.45	$273.50
Purchase #7	$17.69	4.200%	$18.433	$18.43	$18.45	$18.40
7 purchase totals =	$603.73		$669.5285	$669.53	$669.50	$669.40