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	$114.79	11.423%	$127.9025	$127.90	$127.90	$127.90
Purchase #2	$92.64	7.309%	$99.4111	$99.41	$99.40	$99.40
Purchase #3	$139.59	11.112%	$155.1012	$155.10	$155.10	$155.10
Purchase #4	$57.74	5.166%	$60.7228	$60.72	$60.70	$60.70
Purchase #5	$108.56	13.710%	$123.4436	$123.44	$123.45	$123.40
Purchase #6	$175.89	4.223%	$183.3178	$183.32	$183.30	$183.30
Purchase #7	$207.68	5.510%	$219.1232	$219.12	$219.10	$219.10
7 purchase totals =	$896.89		$969.0222	$969.01	$968.95	$968.90