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	$150.62	9.265%	$164.5749	$164.57	$164.55	$164.60
Purchase #2	$225.53	6.495%	$240.1782	$240.18	$240.20	$240.20
Purchase #3	$92.71	11.661%	$103.5209	$103.52	$103.50	$103.50
Purchase #4	$107.99	7.209%	$115.775	$115.78	$115.80	$115.80
Purchase #5	$98.31	7.667%	$105.8474	$105.85	$105.85	$105.80
Purchase #6	$134.49	6.281%	$142.9373	$142.94	$142.95	$142.90
Purchase #7	$18.66	5.721%	$19.7275	$19.73	$19.75	$19.70
7 purchase totals =	$828.31		$892.5612	$892.57	$892.60	$892.50