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	$60.82	5.514%	$64.1736	$64.17	$64.15	$64.20
Purchase #2	$76.62	3.509%	$79.3086	$79.31	$79.30	$79.30
Purchase #3	$48.48	10.275%	$53.4613	$53.46	$53.45	$53.50
Purchase #4	$145.85	3.615%	$151.1225	$151.12	$151.10	$151.10
Purchase #5	$77.93	10.601%	$86.1914	$86.19	$86.20	$86.20
Purchase #6	$120.92	7.638%	$130.1559	$130.16	$130.15	$130.20
Purchase #7	$59.45	5.738%	$62.8612	$62.86	$62.85	$62.90
7 purchase totals =	$590.07		$627.2745	$627.27	$627.20	$627.40