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	$90.71	9.531%	$99.3556	$99.36	$99.35	$99.40
Purchase #2	$213.70	11.595%	$238.4785	$238.48	$238.50	$238.50
Purchase #3	$125.47	3.721%	$130.1387	$130.14	$130.15	$130.10
Purchase #4	$184.29	5.186%	$193.8473	$193.85	$193.85	$193.80
Purchase #5	$5.32	11.184%	$5.915	$5.92	$5.90	$5.90
Purchase #6	$133.51	13.595%	$151.6607	$151.66	$151.65	$151.70
Purchase #7	$105.71	3.160%	$109.0504	$109.05	$109.05	$109.10
7 purchase totals =	$858.71		$928.4462	$928.46	$928.45	$928.50