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	$85.60	5.234%	$90.0803	$90.08	$90.10	$90.10
Purchase #2	$64.71	11.294%	$72.0183	$72.02	$72.00	$72.00
Purchase #3	$245.30	7.162%	$262.8684	$262.87	$262.85	$262.90
Purchase #4	$207.37	11.196%	$230.5871	$230.59	$230.60	$230.60
Purchase #5	$115.80	13.534%	$131.4724	$131.47	$131.45	$131.50
Purchase #6	$84.39	3.166%	$87.0618	$87.06	$87.05	$87.10
Purchase #7	$81.83	9.841%	$89.8829	$89.88	$89.90	$89.90
7 purchase totals =	$885.00		$963.9712	$963.97	$963.95	$964.10