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	$13.89	8.504%	$15.0712	$15.07	$15.05	$15.10
Purchase #2	$57.80	3.427%	$59.7808	$59.78	$59.80	$59.80
Purchase #3	$199.90	9.463%	$218.8165	$218.82	$218.80	$218.80
Purchase #4	$243.47	13.865%	$277.2271	$277.23	$277.25	$277.20
Purchase #5	$118.37	4.805%	$124.0577	$124.06	$124.05	$124.10
Purchase #6	$74.39	6.317%	$79.0892	$79.09	$79.10	$79.10
Purchase #7	$218.90	6.656%	$233.47	$233.47	$233.45	$233.50
7 purchase totals =	$926.72		$1,007.5125	$1,007.52	$1,007.50	$1,007.60