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	$35.31	8.614%	$38.3516	$38.35	$38.35	$38.40
Purchase #2	$142.69	8.537%	$154.8714	$154.87	$154.85	$154.90
Purchase #3	$36.66	12.341%	$41.1842	$41.18	$41.20	$41.20
Purchase #4	$66.39	7.647%	$71.4668	$71.47	$71.45	$71.50
Purchase #5	$60.43	4.106%	$62.9113	$62.91	$62.90	$62.90
Purchase #6	$208.58	13.673%	$237.0991	$237.10	$237.10	$237.10
Purchase #7	$50.61	8.522%	$54.923	$54.92	$54.90	$54.90
7 purchase totals =	$600.67		$660.8074	$660.80	$660.75	$660.90