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	$80.90	9.407%	$88.5103	$88.51	$88.50	$88.50
Purchase #2	$231.57	13.388%	$262.5726	$262.57	$262.55	$262.60
Purchase #3	$78.49	7.175%	$84.1217	$84.12	$84.10	$84.10
Purchase #4	$108.39	5.594%	$114.4533	$114.45	$114.45	$114.50
Purchase #5	$141.49	4.409%	$147.7283	$147.73	$147.75	$147.70
Purchase #6	$129.69	12.691%	$146.149	$146.15	$146.15	$146.10
Purchase #7	$234.38	3.714%	$243.0849	$243.08	$243.10	$243.10
7 purchase totals =	$1,004.91		$1,086.6201	$1,086.61	$1,086.60	$1,086.60