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	$93.28	6.560%	$99.3992	$99.40	$99.40	$99.40
Purchase #2	$95.87	3.268%	$99.003	$99.00	$99.00	$99.00
Purchase #3	$174.90	6.218%	$185.7753	$185.78	$185.80	$185.80
Purchase #4	$28.69	8.763%	$31.2041	$31.20	$31.20	$31.20
Purchase #5	$234.66	6.128%	$249.04	$249.04	$249.05	$249.00
Purchase #6	$15.57	12.155%	$17.4625	$17.46	$17.45	$17.50
Purchase #7	$46.40	3.757%	$48.1432	$48.14	$48.15	$48.10
7 purchase totals =	$689.37		$730.0273	$730.02	$730.05	$730.00