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	$249.50	5.833%	$264.0533	$264.05	$264.05	$264.10
Purchase #2	$80.72	13.460%	$91.5849	$91.58	$91.60	$91.60
Purchase #3	$61.91	7.860%	$66.7761	$66.78	$66.80	$66.80
Purchase #4	$95.59	11.430%	$106.5159	$106.52	$106.50	$106.50
Purchase #5	$231.98	8.490%	$251.6751	$251.68	$251.70	$251.70
Purchase #6	$40.39	11.602%	$45.076	$45.08	$45.10	$45.10
Purchase #7	$168.73	3.218%	$174.1597	$174.16	$174.15	$174.20
7 purchase totals =	$928.82		$999.8410	$999.85	$999.90	$1,000.00