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	$24.92	10.704%	$27.5874	$27.59	$27.60	$27.60
Purchase #2	$219.46	13.539%	$249.1727	$249.17	$249.15	$249.20
Purchase #3	$229.91	8.332%	$249.0661	$249.07	$249.05	$249.10
Purchase #4	$88.60	4.494%	$92.5817	$92.58	$92.60	$92.60
Purchase #5	$176.40	7.177%	$189.0602	$189.06	$189.05	$189.10
Purchase #6	$127.32	3.111%	$131.2809	$131.28	$131.30	$131.30
Purchase #7	$63.99	13.634%	$72.7144	$72.71	$72.70	$72.70
7 purchase totals =	$930.60		$1,011.4634	$1,011.46	$1,011.45	$1,011.60