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	$109.69	13.289%	$124.2667	$124.27	$124.25	$124.30
Purchase #2	$149.38	13.249%	$169.1714	$169.17	$169.15	$169.20
Purchase #3	$222.84	13.490%	$252.9011	$252.90	$252.90	$252.90
Purchase #4	$42.90	3.488%	$44.3964	$44.40	$44.40	$44.40
Purchase #5	$93.98	5.826%	$99.4553	$99.46	$99.45	$99.50
Purchase #6	$21.68	7.835%	$23.3786	$23.38	$23.40	$23.40
Purchase #7	$105.45	5.735%	$111.4976	$111.50	$111.50	$111.50
7 purchase totals =	$745.92		$825.0671	$825.08	$825.05	$825.20