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	$139.71	11.740%	$156.112	$156.11	$156.10	$156.10
Purchase #2	$40.99	3.156%	$42.2836	$42.28	$42.30	$42.30
Purchase #3	$161.77	12.330%	$181.7162	$181.72	$181.70	$181.70
Purchase #4	$27.46	7.162%	$29.4267	$29.43	$29.45	$29.40
Purchase #5	$82.30	13.867%	$93.7125	$93.71	$93.70	$93.70
Purchase #6	$234.27	6.561%	$249.6405	$249.64	$249.65	$249.60
Purchase #7	$58.38	5.561%	$61.6265	$61.63	$61.65	$61.60
7 purchase totals =	$744.88		$814.5180	$814.52	$814.55	$814.40