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	$28.89	4.317%	$30.1372	$30.14	$30.15	$30.10
Purchase #2	$83.88	5.407%	$88.4154	$88.42	$88.40	$88.40
Purchase #3	$54.97	7.516%	$59.1015	$59.10	$59.10	$59.10
Purchase #4	$39.39	4.232%	$41.057	$41.06	$41.05	$41.10
Purchase #5	$188.45	13.451%	$213.7984	$213.80	$213.80	$213.80
Purchase #6	$193.62	11.462%	$215.8127	$215.81	$215.80	$215.80
Purchase #7	$11.75	3.693%	$12.1839	$12.18	$12.20	$12.20
7 purchase totals =	$600.95		$660.5061	$660.51	$660.50	$660.50