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	$128.35	11.397%	$142.978	$142.98	$143.00	$143.00
Purchase #2	$135.86	7.463%	$145.9992	$146.00	$146.00	$146.00
Purchase #3	$186.43	4.303%	$194.4521	$194.45	$194.45	$194.50
Purchase #4	$96.86	8.687%	$105.2742	$105.27	$105.25	$105.30
Purchase #5	$79.37	13.783%	$90.3096	$90.31	$90.30	$90.30
Purchase #6	$127.42	10.431%	$140.7112	$140.71	$140.70	$140.70
Purchase #7	$127.84	8.438%	$138.6271	$138.63	$138.65	$138.60
7 purchase totals =	$882.13		$958.3514	$958.35	$958.35	$958.40