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	$123.53	10.526%	$136.5328	$136.53	$136.55	$136.50
Purchase #2	$165.86	3.294%	$171.3234	$171.32	$171.30	$171.30
Purchase #3	$152.38	3.159%	$157.1937	$157.19	$157.20	$157.20
Purchase #4	$80.58	11.671%	$89.9845	$89.98	$90.00	$90.00
Purchase #5	$72.40	10.610%	$80.0816	$80.08	$80.10	$80.10
Purchase #6	$152.62	3.810%	$158.4348	$158.43	$158.45	$158.40
Purchase #7	$74.47	10.590%	$82.3564	$82.36	$82.35	$82.40
7 purchase totals =	$821.84		$875.9072	$875.89	$875.95	$875.90