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	$116.86	3.380%	$120.8099	$120.81	$120.80	$120.80
Purchase #2	$17.42	8.449%	$18.8918	$18.89	$18.90	$18.90
Purchase #3	$123.34	7.720%	$132.8618	$132.86	$132.85	$132.90
Purchase #4	$12.83	11.637%	$14.323	$14.32	$14.30	$14.30
Purchase #5	$59.95	4.183%	$62.4577	$62.46	$62.45	$62.50
Purchase #6	$114.35	5.404%	$120.5295	$120.53	$120.55	$120.50
Purchase #7	$148.46	3.597%	$153.8001	$153.80	$153.80	$153.80
7 purchase totals =	$593.21		$623.6738	$623.67	$623.65	$623.70