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	$158.63	13.800%	$180.5209	$180.52	$180.50	$180.50
Purchase #2	$82.48	9.613%	$90.4088	$90.41	$90.40	$90.40
Purchase #3	$84.25	13.386%	$95.5277	$95.53	$95.55	$95.50
Purchase #4	$78.85	12.394%	$88.6227	$88.62	$88.60	$88.60
Purchase #5	$147.38	9.615%	$161.5506	$161.55	$161.55	$161.60
Purchase #6	$102.70	13.533%	$116.5984	$116.60	$116.60	$116.60
Purchase #7	$222.73	12.656%	$250.9187	$250.92	$250.90	$250.90
7 purchase totals =	$877.02		$984.1478	$984.15	$984.10	$984.10