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	$60.51	9.848%	$66.469	$66.47	$66.45	$66.50
Purchase #2	$140.91	7.765%	$151.8517	$151.85	$151.85	$151.90
Purchase #3	$103.70	11.717%	$115.8505	$115.85	$115.85	$115.90
Purchase #4	$54.51	5.302%	$57.4001	$57.40	$57.40	$57.40
Purchase #5	$179.74	6.269%	$191.0079	$191.01	$191.00	$191.00
Purchase #6	$70.50	5.341%	$74.2654	$74.27	$74.25	$74.30
Purchase #7	$181.59	8.239%	$196.5512	$196.55	$196.55	$196.60
7 purchase totals =	$791.46		$853.3958	$853.40	$853.35	$853.60