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	$20.90	4.454%	$21.8309	$21.83	$21.85	$21.80
Purchase #2	$73.61	6.107%	$78.1054	$78.11	$78.10	$78.10
Purchase #3	$233.26	11.613%	$260.3485	$260.35	$260.35	$260.30
Purchase #4	$122.48	13.770%	$139.3455	$139.35	$139.35	$139.30
Purchase #5	$164.71	5.390%	$173.5879	$173.59	$173.60	$173.60
Purchase #6	$52.90	9.410%	$57.8779	$57.88	$57.90	$57.90
Purchase #7	$93.63	7.797%	$100.9303	$100.93	$100.95	$100.90
7 purchase totals =	$761.49		$832.0264	$832.04	$832.10	$831.90