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	$36.98	6.181%	$39.2657	$39.27	$39.25	$39.30
Purchase #2	$210.38	4.126%	$219.0603	$219.06	$219.05	$219.10
Purchase #3	$45.42	7.492%	$48.8229	$48.82	$48.80	$48.80
Purchase #4	$43.38	4.355%	$45.2692	$45.27	$45.25	$45.30
Purchase #5	$66.45	9.461%	$72.7368	$72.74	$72.75	$72.70
Purchase #6	$212.83	12.770%	$240.0084	$240.01	$240.00	$240.00
Purchase #7	$106.30	10.392%	$117.3467	$117.35	$117.35	$117.30
7 purchase totals =	$721.74		$782.5100	$782.52	$782.45	$782.50