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	$238.43	6.835%	$254.7267	$254.73	$254.75	$254.70
Purchase #2	$134.87	5.662%	$142.5063	$142.51	$142.50	$142.50
Purchase #3	$47.83	8.858%	$52.0668	$52.07	$52.05	$52.10
Purchase #4	$203.42	7.159%	$217.9828	$217.98	$218.00	$218.00
Purchase #5	$137.28	12.413%	$154.3206	$154.32	$154.30	$154.30
Purchase #6	$66.89	6.185%	$71.0271	$71.03	$71.05	$71.00
Purchase #7	$172.50	13.675%	$196.0894	$196.09	$196.10	$196.10
7 purchase totals =	$1,001.22		$1,088.7197	$1,088.73	$1,088.75	$1,088.70