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	$155.77	7.740%	$167.8266	$167.83	$167.85	$167.80
Purchase #2	$245.49	10.856%	$272.1404	$272.14	$272.15	$272.10
Purchase #3	$101.61	4.209%	$105.8868	$105.89	$105.90	$105.90
Purchase #4	$207.28	12.629%	$233.4574	$233.46	$233.45	$233.50
Purchase #5	$162.99	9.373%	$178.2671	$178.27	$178.25	$178.30
Purchase #6	$59.70	13.723%	$67.8926	$67.89	$67.90	$67.90
Purchase #7	$243.38	8.399%	$263.8215	$263.82	$263.80	$263.80
7 purchase totals =	$1,176.22		$1,289.2924	$1,289.30	$1,289.30	$1,289.30