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	$27.46	6.579%	$29.2666	$29.27	$29.25	$29.30
Purchase #2	$248.33	12.801%	$280.1187	$280.12	$280.10	$280.10
Purchase #3	$61.25	9.334%	$66.9671	$66.97	$66.95	$67.00
Purchase #4	$52.86	11.121%	$58.7386	$58.74	$58.75	$58.70
Purchase #5	$133.45	3.247%	$137.7831	$137.78	$137.80	$137.80
Purchase #6	$151.93	9.107%	$165.7663	$165.77	$165.75	$165.80
Purchase #7	$243.90	8.824%	$265.4217	$265.42	$265.40	$265.40
7 purchase totals =	$919.18		$1,004.0621	$1,004.07	$1,004.00	$1,004.10