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	$25.39	9.846%	$27.8899	$27.89	$27.90	$27.90
Purchase #2	$169.45	9.665%	$185.8273	$185.83	$185.85	$185.80
Purchase #3	$169.82	10.678%	$187.9534	$187.95	$187.95	$188.00
Purchase #4	$41.38	5.865%	$43.8069	$43.81	$43.80	$43.80
Purchase #5	$80.90	3.524%	$83.7509	$83.75	$83.75	$83.80
Purchase #6	$42.51	7.593%	$45.7378	$45.74	$45.75	$45.70
Purchase #7	$188.55	11.723%	$210.6537	$210.65	$210.65	$210.70
7 purchase totals =	$718.00		$785.6199	$785.62	$785.65	$785.70