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	$134.30	13.578%	$152.5353	$152.54	$152.55	$152.50
Purchase #2	$169.71	3.868%	$176.2744	$176.27	$176.25	$176.30
Purchase #3	$72.25	11.257%	$80.3832	$80.38	$80.40	$80.40
Purchase #4	$72.36	5.386%	$76.2573	$76.26	$76.25	$76.30
Purchase #5	$226.28	12.661%	$254.9293	$254.93	$254.95	$254.90
Purchase #6	$166.67	13.763%	$189.6088	$189.61	$189.60	$189.60
Purchase #7	$48.99	8.839%	$53.3202	$53.32	$53.30	$53.30
7 purchase totals =	$890.56		$983.3085	$983.31	$983.30	$983.30