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	$91.48	3.127%	$94.3406	$94.34	$94.35	$94.30
Purchase #2	$123.75	3.145%	$127.6419	$127.64	$127.65	$127.60
Purchase #3	$32.87	11.206%	$36.5534	$36.55	$36.55	$36.60
Purchase #4	$146.51	6.197%	$155.5892	$155.59	$155.60	$155.60
Purchase #5	$197.39	12.390%	$221.8466	$221.85	$221.85	$221.80
Purchase #6	$21.49	12.874%	$24.2566	$24.26	$24.25	$24.30
Purchase #7	$203.72	3.134%	$210.1046	$210.10	$210.10	$210.10
7 purchase totals =	$817.21		$870.3329	$870.33	$870.35	$870.30