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	$148.92	5.373%	$156.9215	$156.92	$156.90	$156.90
Purchase #2	$99.95	5.674%	$105.6212	$105.62	$105.60	$105.60
Purchase #3	$32.52	12.394%	$36.5505	$36.55	$36.55	$36.60
Purchase #4	$29.54	10.594%	$32.6695	$32.67	$32.65	$32.70
Purchase #5	$104.31	10.707%	$115.4785	$115.48	$115.50	$115.50
Purchase #6	$35.86	13.184%	$40.5878	$40.59	$40.60	$40.60
Purchase #7	$184.70	6.175%	$196.1052	$196.11	$196.10	$196.10
7 purchase totals =	$635.80		$683.9342	$683.94	$683.90	$684.00