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	$50.26	11.151%	$55.8645	$55.86	$55.85	$55.90
Purchase #2	$160.89	8.594%	$174.7169	$174.72	$174.70	$174.70
Purchase #3	$80.58	6.243%	$85.6106	$85.61	$85.60	$85.60
Purchase #4	$137.54	13.678%	$156.3527	$156.35	$156.35	$156.40
Purchase #5	$42.83	9.490%	$46.8946	$46.89	$46.90	$46.90
Purchase #6	$157.85	5.589%	$166.6722	$166.67	$166.65	$166.70
Purchase #7	$226.29	5.332%	$238.3558	$238.36	$238.35	$238.40
7 purchase totals =	$856.24		$924.4673	$924.46	$924.40	$924.60