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	$15.90	7.805%	$17.141	$17.14	$17.15	$17.10
Purchase #2	$119.48	6.342%	$127.0574	$127.06	$127.05	$127.10
Purchase #3	$142.46	9.568%	$156.0906	$156.09	$156.10	$156.10
Purchase #4	$33.67	12.368%	$37.8343	$37.83	$37.85	$37.80
Purchase #5	$105.33	3.459%	$108.9734	$108.97	$108.95	$109.00
Purchase #6	$230.42	9.243%	$251.7177	$251.72	$251.70	$251.70
Purchase #7	$67.50	4.106%	$70.2716	$70.27	$70.25	$70.30
7 purchase totals =	$714.76		$769.0860	$769.08	$769.05	$769.10