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	$202.88	9.475%	$222.1029	$222.10	$222.10	$222.10
Purchase #2	$220.81	3.346%	$228.1983	$228.20	$228.20	$228.20
Purchase #3	$104.98	6.214%	$111.5035	$111.50	$111.50	$111.50
Purchase #4	$121.47	13.350%	$137.6862	$137.69	$137.70	$137.70
Purchase #5	$77.80	13.732%	$88.4835	$88.48	$88.50	$88.50
Purchase #6	$76.32	8.104%	$82.505	$82.51	$82.50	$82.50
Purchase #7	$17.76	4.577%	$18.5729	$18.57	$18.55	$18.60
7 purchase totals =	$822.02		$889.0523	$889.05	$889.05	$889.10