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	$134.36	8.271%	$145.4729	$145.47	$145.45	$145.50
Purchase #2	$234.78	10.373%	$259.1337	$259.13	$259.15	$259.10
Purchase #3	$29.77	12.540%	$33.5032	$33.50	$33.50	$33.50
Purchase #4	$25.98	10.734%	$28.7687	$28.77	$28.75	$28.80
Purchase #5	$179.87	6.515%	$191.5885	$191.59	$191.60	$191.60
Purchase #6	$25.59	8.552%	$27.7785	$27.78	$27.80	$27.80
Purchase #7	$201.30	10.479%	$222.3942	$222.39	$222.40	$222.40
7 purchase totals =	$831.65		$908.6397	$908.63	$908.65	$908.70