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	$38.54	6.161%	$40.9144	$40.91	$40.90	$40.90
Purchase #2	$245.42	7.126%	$262.9086	$262.91	$262.90	$262.90
Purchase #3	$20.25	7.379%	$21.7442	$21.74	$21.75	$21.70
Purchase #4	$233.93	7.195%	$250.7613	$250.76	$250.75	$250.80
Purchase #5	$226.83	5.686%	$239.7276	$239.73	$239.75	$239.70
Purchase #6	$43.43	4.188%	$45.2488	$45.25	$45.25	$45.20
Purchase #7	$80.62	12.373%	$90.5951	$90.60	$90.60	$90.60
7 purchase totals =	$889.02		$951.9000	$951.90	$951.90	$951.80