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	$132.41	5.256%	$139.3695	$139.37	$139.35	$139.40
Purchase #2	$162.30	3.423%	$167.8555	$167.86	$167.85	$167.90
Purchase #3	$61.88	9.492%	$67.7536	$67.75	$67.75	$67.80
Purchase #4	$124.65	3.323%	$128.7921	$128.79	$128.80	$128.80
Purchase #5	$111.52	7.768%	$120.1829	$120.18	$120.20	$120.20
Purchase #6	$59.75	4.701%	$62.5588	$62.56	$62.55	$62.60
Purchase #7	$217.66	3.515%	$225.3107	$225.31	$225.30	$225.30
7 purchase totals =	$870.17		$911.8231	$911.82	$911.80	$912.00