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	$137.45	8.688%	$149.3917	$149.39	$149.40	$149.40
Purchase #2	$159.50	11.779%	$178.2875	$178.29	$178.30	$178.30
Purchase #3	$128.58	10.553%	$142.149	$142.15	$142.15	$142.10
Purchase #4	$138.30	3.842%	$143.6135	$143.61	$143.60	$143.60
Purchase #5	$115.59	11.104%	$128.4251	$128.43	$128.45	$128.40
Purchase #6	$167.68	13.165%	$189.7551	$189.76	$189.75	$189.80
Purchase #7	$20.59	4.164%	$21.4474	$21.45	$21.45	$21.40
7 purchase totals =	$867.69		$953.0693	$953.08	$953.10	$953.00