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	$214.53	12.291%	$240.8979	$240.90	$240.90	$240.90
Purchase #2	$152.99	3.708%	$158.6629	$158.66	$158.65	$158.70
Purchase #3	$127.71	4.212%	$133.0891	$133.09	$133.10	$133.10
Purchase #4	$48.88	12.873%	$55.1723	$55.17	$55.15	$55.20
Purchase #5	$156.83	3.860%	$162.8836	$162.88	$162.90	$162.90
Purchase #6	$12.39	13.871%	$14.1086	$14.11	$14.10	$14.10
Purchase #7	$196.51	8.597%	$213.404	$213.40	$213.40	$213.40
7 purchase totals =	$909.84		$978.2184	$978.21	$978.20	$978.30