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	$42.48	3.339%	$43.8984	$43.90	$43.90	$43.90
Purchase #2	$49.82	5.213%	$52.4171	$52.42	$52.40	$52.40
Purchase #3	$179.37	11.448%	$199.9043	$199.90	$199.90	$199.90
Purchase #4	$75.92	4.712%	$79.4974	$79.50	$79.50	$79.50
Purchase #5	$247.74	13.573%	$281.3658	$281.37	$281.35	$281.40
Purchase #6	$64.92	9.849%	$71.314	$71.31	$71.30	$71.30
Purchase #7	$130.50	8.495%	$141.586	$141.59	$141.60	$141.60
7 purchase totals =	$790.75		$869.9830	$869.99	$869.95	$870.00