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	$39.43	7.500%	$42.3873	$42.39	$42.40	$42.40
Purchase #2	$174.38	8.622%	$189.415	$189.42	$189.40	$189.40
Purchase #3	$196.27	5.728%	$207.5123	$207.51	$207.50	$207.50
Purchase #4	$96.63	9.710%	$106.0128	$106.01	$106.00	$106.00
Purchase #5	$22.63	6.172%	$24.0267	$24.03	$24.05	$24.00
Purchase #6	$111.53	10.823%	$123.6009	$123.60	$123.60	$123.60
Purchase #7	$205.46	13.676%	$233.5587	$233.56	$233.55	$233.60
7 purchase totals =	$846.33		$926.5137	$926.52	$926.50	$926.50