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	$103.87	5.448%	$109.5288	$109.53	$109.55	$109.50
Purchase #2	$16.82	11.773%	$18.8002	$18.80	$18.80	$18.80
Purchase #3	$154.82	6.349%	$164.6495	$164.65	$164.65	$164.60
Purchase #4	$195.69	12.391%	$219.9379	$219.94	$219.95	$219.90
Purchase #5	$42.49	5.843%	$44.9727	$44.97	$44.95	$45.00
Purchase #6	$249.71	7.739%	$269.0351	$269.04	$269.05	$269.00
Purchase #7	$155.72	10.843%	$172.6047	$172.60	$172.60	$172.60
7 purchase totals =	$919.12		$999.5289	$999.53	$999.55	$999.40