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	$139.46	13.519%	$158.3136	$158.31	$158.30	$158.30
Purchase #2	$173.53	9.809%	$190.5516	$190.55	$190.55	$190.60
Purchase #3	$165.73	10.752%	$183.5493	$183.55	$183.55	$183.50
Purchase #4	$28.27	7.874%	$30.496	$30.50	$30.50	$30.50
Purchase #5	$151.55	3.358%	$156.639	$156.64	$156.65	$156.60
Purchase #6	$29.31	8.152%	$31.6994	$31.70	$31.70	$31.70
Purchase #7	$137.84	5.424%	$145.3164	$145.32	$145.30	$145.30
7 purchase totals =	$825.69		$896.5653	$896.57	$896.55	$896.50