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	$68.93	13.730%	$78.3941	$78.39	$78.40	$78.40
Purchase #2	$17.75	3.496%	$18.3705	$18.37	$18.35	$18.40
Purchase #3	$124.62	11.591%	$139.0647	$139.06	$139.05	$139.10
Purchase #4	$26.46	5.521%	$27.9209	$27.92	$27.90	$27.90
Purchase #5	$62.75	11.440%	$69.9286	$69.93	$69.95	$69.90
Purchase #6	$72.54	12.233%	$81.4138	$81.41	$81.40	$81.40
Purchase #7	$112.88	5.823%	$119.453	$119.45	$119.45	$119.50
7 purchase totals =	$485.93		$534.5456	$534.53	$534.50	$534.60