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	$17.85	13.266%	$20.218	$20.22	$20.20	$20.20
Purchase #2	$201.81	10.428%	$222.8547	$222.85	$222.85	$222.90
Purchase #3	$5.25	12.295%	$5.8955	$5.90	$5.90	$5.90
Purchase #4	$60.30	5.520%	$63.6286	$63.63	$63.65	$63.60
Purchase #5	$48.30	10.441%	$53.343	$53.34	$53.35	$53.30
Purchase #6	$103.99	7.223%	$111.5012	$111.50	$111.50	$111.50
Purchase #7	$121.74	12.593%	$137.0707	$137.07	$137.05	$137.10
7 purchase totals =	$559.24		$614.5117	$614.51	$614.50	$614.50