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	$245.91	3.658%	$254.9054	$254.91	$254.90	$254.90
Purchase #2	$72.32	8.726%	$78.6306	$78.63	$78.65	$78.60
Purchase #3	$117.46	8.461%	$127.3983	$127.40	$127.40	$127.40
Purchase #4	$46.41	13.124%	$52.5008	$52.50	$52.50	$52.50
Purchase #5	$176.25	5.268%	$185.5349	$185.53	$185.55	$185.50
Purchase #6	$5.50	10.304%	$6.0667	$6.07	$6.05	$6.10
Purchase #7	$66.47	6.824%	$71.0059	$71.01	$71.00	$71.00
7 purchase totals =	$730.32		$776.0426	$776.05	$776.05	$776.00