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	$151.52	5.853%	$160.3885	$160.39	$160.40	$160.40
Purchase #2	$179.46	6.554%	$191.2218	$191.22	$191.20	$191.20
Purchase #3	$237.89	7.438%	$255.5843	$255.58	$255.60	$255.60
Purchase #4	$147.93	13.387%	$167.7334	$167.73	$167.75	$167.70
Purchase #5	$157.70	13.866%	$179.5667	$179.57	$179.55	$179.60
Purchase #6	$74.39	8.642%	$80.8188	$80.82	$80.80	$80.80
Purchase #7	$130.64	9.375%	$142.8875	$142.89	$142.90	$142.90
7 purchase totals =	$1,079.53		$1,178.2010	$1,178.20	$1,178.20	$1,178.20