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	$226.97	12.407%	$255.1302	$255.13	$255.15	$255.10
Purchase #2	$154.44	6.256%	$164.1018	$164.10	$164.10	$164.10
Purchase #3	$236.83	5.218%	$249.1878	$249.19	$249.20	$249.20
Purchase #4	$106.34	3.115%	$109.6525	$109.65	$109.65	$109.70
Purchase #5	$155.47	8.265%	$168.3196	$168.32	$168.30	$168.30
Purchase #6	$89.76	12.456%	$100.9405	$100.94	$100.95	$100.90
Purchase #7	$32.50	4.739%	$34.0402	$34.04	$34.05	$34.00
7 purchase totals =	$1,002.31		$1,081.3726	$1,081.37	$1,081.40	$1,081.30