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	$131.70	10.558%	$145.6049	$145.60	$145.60	$145.60
Purchase #2	$154.56	7.739%	$166.5214	$166.52	$166.50	$166.50
Purchase #3	$164.76	6.213%	$174.9965	$175.00	$175.00	$175.00
Purchase #4	$26.37	11.599%	$29.4287	$29.43	$29.45	$29.40
Purchase #5	$40.45	12.365%	$45.4516	$45.45	$45.45	$45.50
Purchase #6	$203.63	9.526%	$223.0278	$223.03	$223.05	$223.00
Purchase #7	$176.99	6.669%	$188.7935	$188.79	$188.80	$188.80
7 purchase totals =	$898.46		$973.8244	$973.82	$973.85	$973.80