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	$73.54	7.145%	$78.7944	$78.79	$78.80	$78.80
Purchase #2	$168.36	4.262%	$175.5355	$175.54	$175.55	$175.50
Purchase #3	$191.91	12.326%	$215.5648	$215.56	$215.55	$215.60
Purchase #4	$224.49	13.162%	$254.0374	$254.04	$254.05	$254.00
Purchase #5	$53.95	3.855%	$56.0298	$56.03	$56.05	$56.00
Purchase #6	$40.99	9.625%	$44.9353	$44.94	$44.95	$44.90
Purchase #7	$67.89	5.523%	$71.6396	$71.64	$71.65	$71.60
7 purchase totals =	$821.13		$896.5368	$896.54	$896.60	$896.40