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	$53.77	11.316%	$59.8546	$59.85	$59.85	$59.90
Purchase #2	$197.34	5.520%	$208.2332	$208.23	$208.25	$208.20
Purchase #3	$64.31	11.641%	$71.7963	$71.80	$71.80	$71.80
Purchase #4	$16.75	6.175%	$17.7843	$17.78	$17.80	$17.80
Purchase #5	$115.79	3.422%	$119.7523	$119.75	$119.75	$119.80
Purchase #6	$13.77	13.349%	$15.6082	$15.61	$15.60	$15.60
Purchase #7	$84.60	4.484%	$88.3935	$88.39	$88.40	$88.40
7 purchase totals =	$546.33		$581.4224	$581.41	$581.45	$581.50