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	$82.26	8.305%	$89.0917	$89.09	$89.10	$89.10
Purchase #2	$110.65	7.501%	$118.9499	$118.95	$118.95	$118.90
Purchase #3	$111.49	12.223%	$125.1174	$125.12	$125.10	$125.10
Purchase #4	$121.45	8.604%	$131.8996	$131.90	$131.90	$131.90
Purchase #5	$101.76	5.714%	$107.5746	$107.57	$107.55	$107.60
Purchase #6	$153.52	9.197%	$167.6392	$167.64	$167.65	$167.60
Purchase #7	$224.29	6.265%	$238.3418	$238.34	$238.35	$238.30
7 purchase totals =	$905.42		$978.6142	$978.61	$978.60	$978.50