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	$30.33	3.769%	$31.4731	$31.47	$31.45	$31.50
Purchase #2	$114.51	11.206%	$127.342	$127.34	$127.35	$127.30
Purchase #3	$133.34	11.182%	$148.2501	$148.25	$148.25	$148.30
Purchase #4	$227.65	10.103%	$250.6495	$250.65	$250.65	$250.60
Purchase #5	$164.94	6.648%	$175.9052	$175.91	$175.90	$175.90
Purchase #6	$53.37	11.213%	$59.3544	$59.35	$59.35	$59.40
Purchase #7	$146.55	9.757%	$160.8489	$160.85	$160.85	$160.80
7 purchase totals =	$870.69		$953.8232	$953.82	$953.80	$953.80