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	$58.56	12.313%	$65.7705	$65.77	$65.75	$65.80
Purchase #2	$179.38	5.542%	$189.3212	$189.32	$189.30	$189.30
Purchase #3	$164.78	9.759%	$180.8609	$180.86	$180.85	$180.90
Purchase #4	$137.90	13.862%	$157.0157	$157.02	$157.00	$157.00
Purchase #5	$97.70	13.866%	$111.2471	$111.25	$111.25	$111.20
Purchase #6	$173.68	13.321%	$196.8159	$196.82	$196.80	$196.80
Purchase #7	$133.43	12.430%	$150.0153	$150.02	$150.00	$150.00
7 purchase totals =	$945.43		$1,051.0466	$1,051.06	$1,050.95	$1,051.00