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	$90.51	9.673%	$99.265	$99.27	$99.25	$99.30
Purchase #2	$25.86	6.126%	$27.4442	$27.44	$27.45	$27.40
Purchase #3	$35.70	13.504%	$40.5209	$40.52	$40.50	$40.50
Purchase #4	$229.61	7.159%	$246.0478	$246.05	$246.05	$246.00
Purchase #5	$173.44	7.316%	$186.1289	$186.13	$186.15	$186.10
Purchase #6	$182.95	13.583%	$207.8001	$207.80	$207.80	$207.80
Purchase #7	$179.72	9.448%	$196.6999	$196.70	$196.70	$196.70
7 purchase totals =	$917.79		$1,003.9068	$1,003.91	$1,003.90	$1,003.80