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	$20.36	4.472%	$21.2705	$21.27	$21.25	$21.30
Purchase #2	$98.84	9.543%	$108.2723	$108.27	$108.25	$108.30
Purchase #3	$241.48	5.675%	$255.184	$255.18	$255.20	$255.20
Purchase #4	$126.93	12.308%	$142.5525	$142.55	$142.55	$142.60
Purchase #5	$141.37	13.283%	$160.1482	$160.15	$160.15	$160.10
Purchase #6	$126.97	5.591%	$134.0689	$134.07	$134.05	$134.10
Purchase #7	$40.34	7.416%	$43.3316	$43.33	$43.35	$43.30
7 purchase totals =	$796.29		$864.8280	$864.82	$864.80	$864.90