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	$156.70	7.146%	$167.8978	$167.90	$167.90	$167.90
Purchase #2	$249.83	11.458%	$278.4555	$278.46	$278.45	$278.50
Purchase #3	$6.75	10.518%	$7.46	$7.46	$7.45	$7.50
Purchase #4	$68.86	9.656%	$75.5091	$75.51	$75.50	$75.50
Purchase #5	$85.64	6.152%	$90.9086	$90.91	$90.90	$90.90
Purchase #6	$13.93	7.373%	$14.9571	$14.96	$14.95	$15.00
Purchase #7	$78.57	8.430%	$85.1935	$85.19	$85.20	$85.20
7 purchase totals =	$660.28		$720.3816	$720.39	$720.35	$720.50