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	$79.98	8.607%	$86.8639	$86.86	$86.85	$86.90
Purchase #2	$140.76	10.463%	$155.4877	$155.49	$155.50	$155.50
Purchase #3	$106.51	13.838%	$121.2489	$121.25	$121.25	$121.20
Purchase #4	$187.77	5.535%	$198.1631	$198.16	$198.15	$198.20
Purchase #5	$106.38	5.713%	$112.4575	$112.46	$112.45	$112.50
Purchase #6	$85.40	6.494%	$90.9459	$90.95	$90.95	$90.90
Purchase #7	$107.69	3.585%	$111.5507	$111.55	$111.55	$111.60
7 purchase totals =	$814.49		$876.7177	$876.72	$876.70	$876.80