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	$56.87	13.261%	$64.4115	$64.41	$64.40	$64.40
Purchase #2	$116.35	11.270%	$129.4626	$129.46	$129.45	$129.50
Purchase #3	$74.59	9.816%	$81.9118	$81.91	$81.90	$81.90
Purchase #4	$127.77	12.640%	$143.9201	$143.92	$143.90	$143.90
Purchase #5	$114.59	11.399%	$127.6521	$127.65	$127.65	$127.70
Purchase #6	$181.27	13.321%	$205.417	$205.42	$205.40	$205.40
Purchase #7	$171.52	8.743%	$186.516	$186.52	$186.50	$186.50
7 purchase totals =	$842.96		$939.2911	$939.29	$939.20	$939.30