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	$234.88	8.727%	$255.378	$255.38	$255.40	$255.40
Purchase #2	$79.49	11.302%	$88.474	$88.47	$88.45	$88.50
Purchase #3	$178.46	12.544%	$200.846	$200.85	$200.85	$200.80
Purchase #4	$127.84	13.862%	$145.5612	$145.56	$145.55	$145.60
Purchase #5	$52.30	12.546%	$58.8616	$58.86	$58.85	$58.90
Purchase #6	$90.80	12.725%	$102.3543	$102.35	$102.35	$102.40
Purchase #7	$130.85	12.696%	$147.4627	$147.46	$147.45	$147.50
7 purchase totals =	$894.62		$998.9378	$998.93	$998.90	$999.10