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	$70.78	13.778%	$80.5321	$80.53	$80.55	$80.50
Purchase #2	$201.74	11.393%	$224.7242	$224.72	$224.70	$224.70
Purchase #3	$106.61	13.698%	$121.2134	$121.21	$121.20	$121.20
Purchase #4	$40.92	7.186%	$43.8605	$43.86	$43.85	$43.90
Purchase #5	$143.63	5.400%	$151.386	$151.39	$151.40	$151.40
Purchase #6	$209.56	6.386%	$222.9425	$222.94	$222.95	$222.90
Purchase #7	$230.57	4.830%	$241.7065	$241.71	$241.70	$241.70
7 purchase totals =	$1,003.81		$1,086.3652	$1,086.36	$1,086.35	$1,086.30