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	$52.32	5.530%	$55.2133	$55.21	$55.20	$55.20
Purchase #2	$207.59	4.721%	$217.3903	$217.39	$217.40	$217.40
Purchase #3	$64.28	13.446%	$72.9231	$72.92	$72.90	$72.90
Purchase #4	$97.27	12.332%	$109.2653	$109.27	$109.25	$109.30
Purchase #5	$132.54	8.337%	$143.5899	$143.59	$143.60	$143.60
Purchase #6	$25.49	4.199%	$26.5603	$26.56	$26.55	$26.60
Purchase #7	$102.53	10.375%	$113.1675	$113.17	$113.15	$113.20
7 purchase totals =	$682.02		$738.1097	$738.11	$738.05	$738.20