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	$127.69	6.172%	$135.571	$135.57	$135.55	$135.60
Purchase #2	$113.86	9.687%	$124.8896	$124.89	$124.90	$124.90
Purchase #3	$97.28	3.540%	$100.7237	$100.72	$100.70	$100.70
Purchase #4	$128.68	9.837%	$141.3383	$141.34	$141.35	$141.30
Purchase #5	$56.25	5.406%	$59.2909	$59.29	$59.30	$59.30
Purchase #6	$246.47	12.768%	$277.9393	$277.94	$277.95	$277.90
Purchase #7	$142.50	11.104%	$158.3232	$158.32	$158.30	$158.30
7 purchase totals =	$912.73		$998.0760	$998.07	$998.05	$998.00