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	$127.87	7.669%	$137.6764	$137.68	$137.70	$137.70
Purchase #2	$96.64	9.394%	$105.7184	$105.72	$105.70	$105.70
Purchase #3	$28.73	11.623%	$32.0693	$32.07	$32.05	$32.10
Purchase #4	$37.43	10.282%	$41.2786	$41.28	$41.30	$41.30
Purchase #5	$63.58	12.282%	$71.3889	$71.39	$71.40	$71.40
Purchase #6	$248.50	12.671%	$279.9874	$279.99	$280.00	$280.00
Purchase #7	$185.89	5.407%	$195.9411	$195.94	$195.95	$195.90
7 purchase totals =	$788.64		$864.0601	$864.07	$864.10	$864.10