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	$82.80	8.278%	$89.6542	$89.65	$89.65	$89.70
Purchase #2	$93.80	10.492%	$103.6415	$103.64	$103.65	$103.60
Purchase #3	$198.46	7.503%	$213.3505	$213.35	$213.35	$213.40
Purchase #4	$90.52	4.523%	$94.6142	$94.61	$94.60	$94.60
Purchase #5	$249.75	10.121%	$275.0272	$275.03	$275.05	$275.00
Purchase #6	$65.49	7.324%	$70.2865	$70.29	$70.30	$70.30
Purchase #7	$120.66	4.832%	$126.4903	$126.49	$126.50	$126.50
7 purchase totals =	$901.48		$973.0644	$973.06	$973.10	$973.10