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	$225.37	9.196%	$246.095	$246.10	$246.10	$246.10
Purchase #2	$51.36	12.858%	$57.9639	$57.96	$57.95	$58.00
Purchase #3	$148.63	7.114%	$159.2035	$159.20	$159.20	$159.20
Purchase #4	$144.63	4.788%	$151.5549	$151.55	$151.55	$151.60
Purchase #5	$139.57	4.153%	$145.3663	$145.37	$145.35	$145.40
Purchase #6	$18.54	12.581%	$20.8725	$20.87	$20.85	$20.90
Purchase #7	$54.27	9.551%	$59.4533	$59.45	$59.45	$59.50
7 purchase totals =	$782.37		$840.5094	$840.50	$840.45	$840.70