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	$71.31	10.511%	$78.8054	$78.81	$78.80	$78.80
Purchase #2	$52.56	13.225%	$59.5111	$59.51	$59.50	$59.50
Purchase #3	$48.43	5.834%	$51.2554	$51.26	$51.25	$51.30
Purchase #4	$165.60	6.783%	$176.8326	$176.83	$176.85	$176.80
Purchase #5	$163.98	4.641%	$171.5903	$171.59	$171.60	$171.60
Purchase #6	$168.34	6.442%	$179.1845	$179.18	$179.20	$179.20
Purchase #7	$39.77	5.658%	$42.0202	$42.02	$42.00	$42.00
7 purchase totals =	$709.99		$759.1995	$759.20	$759.20	$759.20