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	$29.35	8.604%	$31.8753	$31.88	$31.90	$31.90
Purchase #2	$57.38	4.316%	$59.8565	$59.86	$59.85	$59.90
Purchase #3	$220.95	9.462%	$241.8563	$241.86	$241.85	$241.90
Purchase #4	$17.60	12.740%	$19.8422	$19.84	$19.85	$19.80
Purchase #5	$115.38	10.830%	$127.8757	$127.88	$127.90	$127.90
Purchase #6	$200.79	11.809%	$224.5013	$224.50	$224.50	$224.50
Purchase #7	$222.38	8.278%	$240.7886	$240.79	$240.80	$240.80
7 purchase totals =	$863.83		$946.5959	$946.61	$946.65	$946.70