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	$142.43	3.104%	$146.851	$146.85	$146.85	$146.90
Purchase #2	$108.25	7.453%	$116.3179	$116.32	$116.30	$116.30
Purchase #3	$99.75	5.852%	$105.5874	$105.59	$105.60	$105.60
Purchase #4	$115.35	7.120%	$123.5629	$123.56	$123.55	$123.60
Purchase #5	$193.85	10.160%	$213.5452	$213.55	$213.55	$213.50
Purchase #6	$158.43	5.620%	$167.3338	$167.33	$167.35	$167.30
Purchase #7	$100.43	5.341%	$105.794	$105.79	$105.80	$105.80
7 purchase totals =	$918.49		$978.9922	$978.99	$979.00	$979.00