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	$135.85	13.630%	$154.3664	$154.37	$154.35	$154.40
Purchase #2	$248.92	12.553%	$280.1669	$280.17	$280.15	$280.20
Purchase #3	$39.37	3.528%	$40.759	$40.76	$40.75	$40.80
Purchase #4	$91.64	8.808%	$99.7117	$99.71	$99.70	$99.70
Purchase #5	$207.55	6.286%	$220.5966	$220.60	$220.60	$220.60
Purchase #6	$93.29	7.709%	$100.4817	$100.48	$100.50	$100.50
Purchase #7	$197.85	3.175%	$204.1317	$204.13	$204.15	$204.10
7 purchase totals =	$1,014.47		$1,100.2140	$1,100.22	$1,100.20	$1,100.30