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	$44.92	8.727%	$48.8402	$48.84	$48.85	$48.80
Purchase #2	$141.92	13.167%	$160.6066	$160.61	$160.60	$160.60
Purchase #3	$118.55	7.421%	$127.3476	$127.35	$127.35	$127.30
Purchase #4	$43.48	13.316%	$49.2698	$49.27	$49.25	$49.30
Purchase #5	$52.97	5.323%	$55.7896	$55.79	$55.80	$55.80
Purchase #6	$219.56	7.849%	$236.7933	$236.79	$236.80	$236.80
Purchase #7	$50.93	9.746%	$55.8936	$55.89	$55.90	$55.90
7 purchase totals =	$672.33		$734.5407	$734.54	$734.55	$734.50