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	$222.72	11.464%	$248.2526	$248.25	$248.25	$248.30
Purchase #2	$153.52	9.543%	$168.1704	$168.17	$168.15	$168.20
Purchase #3	$219.66	8.542%	$238.4234	$238.42	$238.40	$238.40
Purchase #4	$112.71	13.385%	$127.7962	$127.80	$127.80	$127.80
Purchase #5	$44.61	3.353%	$46.1058	$46.11	$46.10	$46.10
Purchase #6	$156.74	8.280%	$169.7181	$169.72	$169.70	$169.70
Purchase #7	$217.65	10.680%	$240.895	$240.90	$240.90	$240.90
7 purchase totals =	$1,127.61		$1,239.3615	$1,239.37	$1,239.30	$1,239.40